if you used 7tsp to install the theme pack extras then run 7tsp and select the restore button.
the only themes i have used are mr grims and i only use 7tsp for the theme extras.
as jerry said running sfc scan will revert the changes made to system icons ,clock etc. the actual theme you can just switch to windows aero in the personalization window to change the theme back.
im pretty sure when you run mr grims installers there is a warning saying they cant be uninstalled.