You should start by using the Control Panel to "Add/Remove Programs"
Then after you have un-installed the software you can use a program such as
RegCleaner to clean up the rest of the junk.
RegCleaner Publisher's Description:
With RegCleaner you can easily get rid of those old and obsolete registry entries created by software that you have destroyed ages ago.
You don?t have to be an expert to use this program. Note that this program is not like those other so called registry cleaners, they search any filenames from registry, then if the file doesn?t exist anymore they remove the registry key or value where this filename was.
But RegCleaner shows you the list of software that are registered in the registry and by checking checkboxes you select which software you don?t have anymore and RegCleaner removes all registry created by those programs automatically.
You can also remove start up programs that are started behind your back and can dramatically decrease your computer?s performance.