What do I need to do to switch from Ubuntu to Lubuntu on a dual boot computer?

view full story

http://askubuntu.com – I got a new laptop which makes my old one with a dual boot of XP and 11.10 redundant. Everything has been moved over and this is a perfect chance to play around with variants. I would like to replace the Ubuntu with Lubuntu but assume that if I just remove the Ubuntu partition to make room there will be issues with the existing grub. Is there a way to do this? Or as another possibility I could shrink the Ubuntu partition and install something in the empty space. Will an Ubuntu based installer recognize what is going on and set up a triple boot as effortlessly as it does a dual boot? (HowTos)