I should have mentioned this earlier, but there is a package floating
around out there called "GRUB Customizer", that you can use to edit the
menu. It wouldn't have uninstalled the extraneous kernels, I think, but
it can be nice if you are not familiar with GRUBs syntax (which I admit
I don't fully understand, either).
As a side note, if you are trying to learn something about Linux, two
of the best resources I have found are the Arch wiki[1] and the Debian
wiki[2]. Another really nice link is the Debian Administrator's
Handbook[3]. Following random advice and running scripts found on a
forum can be quite dangerous, and often don't tell you *why* you need
to do what you need to do. Look for official documentation.
Petter
[1] https://wiki.archlinux.org/
[2] https://wiki.debian.org/
[3] http://debian-handbook.info/