When Testing an Android App, It runs a Different App

I am trying to make a lite and a premium version of an app. I have finished the lite version and am now working on the premium version. I am trying to test it, but when I try, it runs the lite version instead. It says that it was installing the premium apk, but it runs the lite version anyway. If it's related, I didn't use "Create Project From Existing Code," and when I copied and pasted parts, I made sure not to include the package name. Why is this happening, and how can I fix it?