Safest method (and a damn sight quicker than doing it manually) is to use CCleaner:
http://filehippo.com/download_ccleaner/
The free version is all you need, so click "Download latest version" (first green button at the top).
It also incorporates a Registry Cleaner module - - I advise you not to use that, just use the general cleaner.
It's perfectly safe & won't remove anything that's important or vital.