If the app has an uninstall routine use that. If it doesn't you can use a utility such as AppCleaner. BTW if you have come from the MS Windows world uninstalling apps Macs is really simply just drag them to the trash. Any files left behind will not affect the performance of the system and are normally so small (KB's) that they can be ignored. Tools like AppCleaner are not totally necessary to be honest, they're there to just make us feel better.