Help with array,How to select from a list of arrays?

Hi, learning c# still so bare with me!

I have an array of 19 (20 numbers)

I have a minus and plus button and I want to select from the list of the array using the buttons I feel like I am on the right path and a bit close but I am stuck on what to do!

any help would be much appreciated!

from my understanding the +1 and -1 I am doing is basically adding or subtracting 5000. Instead I want to be able to select from this list 0-19.

 public int[] lineBetsArray = {1000, 5000, 10000, 20000, 30000, 40000, 50000, 75000, 100000, 125000, 150000, 175000, 200000, 250000, 300000, 350000, 400000, 450000, 500000, 1000000};
 
         public void LineBetPlus_Click()
         {
             AddLineBet(lineBetsArray[+1]);
         }
 
         public void LineBetMinus_Click()
         {
             AddLineBet(lineBetsArray[-1]);
         }