Grid based movement, sprite change to simulate movement

Hello,

I am in the process of creating a first person dungeon crawler and I have run into an issue. I am pretty new to the concept of coding so I am sure there is a much easier way to do what I have done but I wasn't sure what the correct coding process was.

Anyway, I am creating a first person dungeon crawler that looks like this:

My idea is in a 9 square grid with each grid square having 4 pictures (North, East, South, West.)

Here is the code I use to change the pictures to depict the feeling of walking:

     public Sprite One_North;
     public Sprite One_East;
     public Sprite One_South;
     public Sprite One_West;
     public Sprite Two_North;
     public Sprite Two_East;
     public Sprite Two_South;
     public Sprite Two_West;
 
     public Image gameplayImageTransition; 
     private DirectionDetection directionDetection;
 
     public string currentTileNumber;
     public string currentDirection;
     public string currentTileAndDirection;
 
     // Use this for initialization
     void Start () {
         currentDirection = "North";
         currentTileNumber = "Two";
         gameplayImageTransition.sprite = Two_North;
     }
     
     // Update is called once per frame
     void Update () {
         if(Input.GetKeyDown(KeyCode.UpArrow)){
             Debug.Log ("Up Arrow");
             UpdateWalkPathForward ();
         }

         if(Input.GetKeyDown(KeyCode.LeftArrow)){
             Debug.Log ("Left Arrow");
             UpdateWalkPathLeft ();
         }
     }
 
     void UpdateWalkPathForward(){
         if (currentDirection == "West") {
             ConvertCurrentTileNumberToInt ();
             int curTileDummy = System.Convert.ToInt32 (currentTileNumber) - 1;
             currentTileNumber = System.Convert.ToString (curTileDummy);
             ConvertCurrentTileNumberToString ();
             gameplayImageTransition.sprite = (Sprite)this.GetType ().GetField (currentTileNumber + "_West").GetValue (this);
         } else if (currentDirection == "East") {
             ConvertCurrentTileNumberToInt ();
             int curTileDummy = System.Convert.ToInt32 (currentTileNumber) + 1;
             currentTileNumber = System.Convert.ToString (curTileDummy);
             ConvertCurrentTileNumberToString ();
             gameplayImageTransition.sprite = (Sprite)this.GetType ().GetField (currentTileNumber + "_East").GetValue (this);
         }
     }
 
     void UpdateWalkPathLeft(){
         if(currentDirection == "North"){
             currentDirection = "West";
             gameplayImageTransition.sprite = (Sprite)this.GetType().GetField(currentTileNumber + "_West").GetValue(this);
         }else if(currentDirection == "West"){
             currentDirection = "South";
             gameplayImageTransition.sprite = (Sprite)this.GetType().GetField(currentTileNumber + "_South").GetValue(this);
         }else if(currentDirection == "South"){
             currentDirection = "East";
             gameplayImageTransition.sprite = (Sprite)this.GetType().GetField(currentTileNumber + "_East").GetValue(this);
         }else if(currentDirection == "East"){
             currentDirection = "North";
             gameplayImageTransition.sprite = (Sprite)this.GetType().GetField(currentTileNumber + "_North").GetValue(this);
         }
     }
  
     public void ConvertCurrentTileNumberToInt(){
         if (currentTileNumber == "One") {
             currentTileNumber = "1";
         }else if (currentTileNumber == "Two") {
             currentTileNumber = "2";
         }
     }
 
     public void ConvertCurrentTileNumberToString(){
         if (currentTileNumber == "1") {
             currentTileNumber = "One";
         }else if (currentTileNumber == "2") {
             currentTileNumber = "Two";
         }
     }
 }
 

So basically you start at Two_North (tile two, facing North) and in my example you press the left arrow which changes the pictures from Two_North to Two_West. Then when you press the Up arrow it will switch the picture from Two_West to One_West like you were walking one square up.

One of the main things I have run into is getting the math to work. So far it works okay but my issue is that if I am on tile four and I'm facing west and press up on the keyboard I will jump from Four_West to Three_West which should not happen. Instead of jumping to the top of the grid the player should just stand in Four_west and not move anywhere (basically like running into a wall.)

If anyone has any tips for me that would be amazing, at this point I am stuck trying to figure out what to do with this. Thank You for your help.