I'd vote for grub instead of lilo too. Grub is easier to maintain (the boot list, if and when you add/upgrade kernels) and when you take a short lesson with it's configuration file syntax, you notice it's at least as easy as lilo's. Lilo is not as easy to handle as grub, and when you alter it's configuration, you need to reinstall it every time again. Also if there's a problem with the configuration file, if you're using Grub you can enter an interactive shell, fix the boot entry, be able to boot it and then fix the configuration for good (changes made in the interactive shell don't get saved to disk as far as I know), but if you're instead using Lilo, you need a bootdisk or a live-cd to get your hands on the configuration file (and be able to reinstall lilo to have the changes apply), because it doesn't have such features as Grub.
To change your bootloader simply obtain and install the one you like, then configure it. It overwrites the previous bootloader (if you install it to the same place, usually MBR).