Swap UI Image from images Folder C#

If I have a folder called "Factoid Images" that is located in Textures/Factoid Images

How can I change that image to a new image from that folder with each:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class FactoidManager : MonoBehaviour {
 
     public Image factoidImagePlaceholder;
     public Sprite[] gallery;    //Store Factoid images in here
     public int i = 0;    //Will Control where in the array we are
 
 
     public Text factoidScreenText;
     public TextAsset factoidText;
     public string[] factoidLines;
 
 
     public int startLine;
     public int endLine;
 
 
     void Start(){
         factoidImagePlaceholder.enabled = false;
         if (factoidText != null) {
             factoidLines = (factoidText.text.Split ('\n'));
         }
 
         if (endLine == 0) {
             endLine = factoidLines.Length - 1;
         }
     }
 
     void Update () {
         factoidImagePlaceholder.sprite = gallery[i];
     }
 
 
 
     //Factoid Calls
     public void  GoFactoid01(){//Billy The Kidd
         factoidScreenText.text = "BILLY THE KIDD\nREAL NAME WILLIAM BONNEY\nBORN: 1860\nDIED: JULY 13, 1881"; //NEEDS to Display multiple lines from the .txt doc
 
         //Swap Image from ""Factoid Images" foldeer Code
         factoidImagePlaceholder.enabled = true;
         i = 2;
 
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid02(){//Darth Vader
         factoidScreenText.text = "DARTH VADER\nALSO KNOWN AS ANAKIN SKYWALKER A FICTIONAL CHARACTER IN THE STAR WARS UNIVERSE.\nCHARACTER CREATED BY DIRECTOR GEORGE LUCAS"; //NEEDS to Display multiple lines from the .txt doc
 
         factoidImagePlaceholder.enabled = true;
         i = 5;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid03(){//Parapsychology
         factoidScreenText.text = "THE STUDY OF MENTAL PHENOMENON THAT ARE EXCLUDED FROM THE OR INEXPLICABLE BY ORTHODOX SCIENTIFIC PSYCHOLOGY SUCH AS HYPNOSIS, TELEPATHY, ETC."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = false;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid04(){//U.F.O.s
         factoidScreenText.text = "AN UNIDENTIFIED FLYING OBJECT, OR U.F.O. IN IT'S MOST GENERAL DEFINITION, IS ANY APPARENT ANOMALY IN THE SKY THAT IS NOT IDENTIFIABLE AS A KNOWN OBJECT OR PHENOMENON."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 11;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid05(){//R2D2
         factoidScreenText.text = "R2D2 or ARTOO-DETOO IS A FICTIONAL CHARACTER IN THE STAR WARS UNIVERSE\nCREATED BY GEORGE LUCAS\nREFERED TO IN THE NOVEL AS A THERMOCAPSULARY DEHOUSING ASSISTER"; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 10;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid06(){//C3PO
         factoidScreenText.text = "C-3PO or SEE-THREEPIO IS A FICTIONAL CHARACTER IN THE STAR WARS UNIVERSE\nCREATED BY GEORGE LUCAS\nPROTOCOL DROID TO ASSIST IN ETIQUETTE, CUSTOMS, AND TRANSLATION."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 3;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid07(){//Ancient Astronaughts
         factoidScreenText.text = "ANCIENT ASTRONAUTS (OR ANCIENT ALIENS) IS A PSEUDOSCIENTIFIC CONCEPT BASED ON THE BELIEF THAT INTELLIGENT EXTRATERRESTRIAL BEINGS VISITED AND MADE CONTACT WITH HUMANS IN PREHISTORIC TIMES"; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 0;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid08(){//Crop Circles
         factoidScreenText.text = "AN AREA OF STANDING CROPS THAT HAS BEEN FLATTENED IN THE FORM OF A CIRCLE OR MORE COMPLEX PATTERN. NO GENERAL CAUSE OF CROP CIRCLES HAS BEEN IDENTIFIED ALTHOUGH VARIOUS NATURAL AND UNORTHODOX EXPLANATIONS HAVE BEEN PUT FORWARD. MANY OF THE CIRCLES ARE KNOW TO BE HOAXES WHILE OTHERS REMAIN UNEXPLAINED."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 4;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid09(){//Big Foot
         factoidScreenText.text = "BIG FOOT (ALSO KNOWN AS SASQUATCH) IS THE NAME GIVEN A MYTHICAL SIMIAN, APE, OR HOMINID-LIKE CREATURE THAT IS SAID TO INHABIT FORESTS, MAINLY IN THE PACIFIC NORTHWEST. IN AMERICAN FOLKLORE, BIGFOOT IS USUALLY DESCRIBED AS A LARGE, HAIRY, BIPEDAL HUMANOID."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 1;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid10(){//Dracula
         factoidScreenText.text = "THOUGH DRACULA IS A PURELY FICTIONAL CREATION, BRAM STOKER NAMED HIS INFAMOUS CHARACTER AFTER A REAL PERSON WHO HAPPENED TO HAVE A TASTE FOR BLOOD: VLAD III, PRINCE OF WALLACHIA OR - AS HE IS BETTER KNOW - VLAD THE IMPALER."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 7;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid11(){//Doc. Brown
         factoidScreenText.text = "EMMETT LATHROP (DOC. BROWN), Ph.D, IS A FICTIONAL CHARACTER IN THE BACK TO THE FUTURE TRILOGY IN WHICH HE IS THE INVENTOR OF THE FIRST TIME MACHINE HE BUILT OUT OF A DELOREAN SPORTS CAR. THE CHARACTER IS PORTRAYED BY CHRISTOPHER LLOYD."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 6;
         StartCoroutine(LoadFactoid());
     }
 
     public void  GoFactoid12(){//Frankenstein
         factoidScreenText.text = "FRANKENSTEIN: OR, THE MODERN PROMETHEUS IS A NOVEL WRITTEN BY ENGLISH AUTHOR MARY WOLLSTONECRAFT SHELLEY THAT TELL THE STORY OF A YOUNG SCIENCE STUDENT VICTOR FRANKENSTEIN, WHO CREATES A GROTESQUE BUT SENTIENT CREATURE IN AN UNORTHODOX SCIENTIFIC EXPERIMENT."; //NEEDS to Display multiple lines from the .txt doc
         factoidImagePlaceholder.enabled = true;
         i = 8;
         StartCoroutine(LoadFactoid());
     }
 
 
     //Factoid Calls
     IEnumerator LoadFactoid(){
         yield return new WaitForSeconds(1.5f); // wait time
         MasterPanelManager mpm = FindObjectOfType<MasterPanelManager>();
         mpm.EnableFactoidPanel();
         CameraSwitcher cs18 = FindObjectOfType<CameraSwitcher>();
         cs18.EnableCamera18();
 
         yield return new WaitForSeconds(15.5f); // wait time
         MasterPanelManager ebd = FindObjectOfType<MasterPanelManager>();
         ebd.DisableFactoidPanel();
         CameraSwitcher csdef = FindObjectOfType<CameraSwitcher>();
         csdef.CameraDefault();
 
     }
 }