How can I change a particular variable to some other throughout the whole program? : How can I change a particular variable to some other throughout the whole program?

I had made a program about a year ago, when I was still a newbie. I have used all types of meaningless variables, which right now, make no sense to me.

For example, I have made an array L which has quantity, and I want to switch L with 'qty' throughout the program!

Find and replace will take forever. Any other method that I can use here?