To uninstall ubuntu-keyboard-spanish just follow these instructions.
Are you having problems? You can always add ubuntu-keyboard-spanishagain by following the instructions at this link.
This will remove just the ubuntu-keyboard-spanish package itself.
This will remove the ubuntu-keyboard-spanish package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for ubuntu-keyboard-spanish then this will work.