How to alter joystick values with Arduino Uno?
if (voltageX &gt;= 4.55) {
  voltageX == 2.5;
  successPin==HIGH;


The last two lines (and all similar ones later) are wrong. == is for comparing, = is for assigning. So change it to:

if (voltageX &gt;= 4.55) {
  voltageX = 2.5;
  successPin = HIGH;


You did that in a lot of places, so fix that up and get back to us.



const int successPin = 13; 
...
  successPin = HIGH;


Assuming you fix the compare to an assign you will get an error message here. You define successPin as 13, and then try to change it to 1 (which is what HIGH is defined as). Do you mean, to write to that pin? Like this?

digitalWrite (successPin, HIGH);  


You will need to change all those as well. And if you are hoping to see an LED on the pin flash, 1 ms is quite a small interval.