how to test Facebook Login for my app

I am adding Facebook login to my app so to get permission to post photos for users. Having created the code, I now want to test that it works. So naturally I am using my own Facebook again to see that the system works. The first time I went through, I found some stuff I didn't like. So I made the changes. Now that I want to test again using my Facebook again, when I login, Facebook keeps telling me that I already gave the app permission. I tried uninstalling the app and then re-install, just in case it was caching locally. But that didn't help. So my question is: how do I get to reuse my account to login and request the permissions again? I hope the question is clear. If not, please ask for clarification.