There are programs that can record all the changes to your systems that are made during installating. You can remove all of them (including registry settings) later on when un-installing. The only problem is that you have to use such programs before installing.

You may also clean your registry with a registry cleaner Lots of them available on the market. I don't really like to use them. I prefer to make a fresh OS installation a couple of times a year.

You may also run regedit and try to find all registry entries related to your software. And then just remove them manually.