How do I change all occurrences of a variable in eclipse in Java simultaneously

I'm currently creating an item framework/categorisation system for a game. The specifics aren't important because the question is very general. I'm often changing the structure of the framework (changing the name of a variable, adding arguments to methods that create specific types of items) and I have to keep on going through all of the occurrences of a variable when I change it and I'm sure there's a way to change all occurrences of a variable without having to go through all occurrences manually but I can't seem to find a way to do it in eclipse or on the internet.