Creating a field that automatically changes to uppercase

Hi, first things first. Assume I know nothing! I have never written code and never used Javascript. I am using Acrobat Pro DC on Windows. I have created a requisition form. In that form I have a field where people will enter two letters. I want those letters to be converted to UPPER CASE if they have been entered in lower case. In the field properties window, I tried to create a custom keystroke script. I clicked on the custom keystroke script editor and inserted event.change = event.change.toUpperCase() which I found in a forum. Then it prompts me to "Go To" and opens another window "Go To Line" where I am to insert something. This is where I am stuck. It seems like such a simple task I am trying to perform and yet....3 hours later...no results. I would really appreciate anyone's help.