When you were a kid, did your parents ever point to your clean room and say, "you missed a spot"? Uninstalling a program works the same way. You'll erase most of it, but your uninstall utility will often "miss a spot."
The left over bits and pieces that you didn't clean off your computer's plate can build up over time. They can even slow down your computer!
If you don't need or want a program anymore, you need to get rid of it all, including the leftovers. Revo Uninstaller is a free download that can do that for you with just one click.
When you download Revo, make sure you scroll down and click the Download button at the bottom of the Freeware column. There's a "Free Trial" download button displayed prominently at the top that will get you a trial version of Revo's paid professional uninstaller, which will ask you to buy a license.
When you open Revo, a list of all your programs will appear. This should remind you a little bit of Windows' stock uninstall utility. And it works similarly to an extent.
When you click uninstall, Revo will ask how thoroughly you want to remove a program. The recommended setting is fine for basic users. It will delete a program using the standard process, then look for any remnants in temporary folders or in the registry.