If you installed Sitecore 8.2 from the .EXE File, just run the uninstaller from Windows, (add or remove programs) and remove the not removed files from the webroot.
But there is uninstall section in the installation manual:
4.6 Uninstalling Sitecore XP
Before uninstalling Sitecore:
Delete the IIS Website or update it to reference a different directory, or stop IIS by executing the following command: o net stop w3svc.
Remove the Sitecore file system.
Remove any databases on remote or local servers that are used by this instance of Sitecore.