[Hampshire] Reset root password

I set my son up a laptop with xubuntu on it and the password I choose for root
was not the normal one I use (because he knows that one). Now the problem is I
can't rememebr what it was either. I want to add a couple of program and update
etc. and I can't now, my son is not setup as a sudoer user so that not an
option.

Can anybody point me in the direction of a set of instructions for password
recovery that work, I have googled but there are many but I don't want to end
up damaging the install trying to reset the password so I am looking for
instruction that other have used without a problem.

Thanks

Tim