you can use a number of editors, the most common or what i prefer for quick edits is vi... it can be taunting at first to use.. but you would open a file like lilo.conf in this case as:
your going to want to look up some common commands to use vi, like I puts you in Interactive mode and then you can edit..
to save you can do a ctrl + ZZ after editing the file.
man vi for more info.. and there are many others.. like pico, jed.. etc..
and just a FYI, always to make changes after editing lilo, run lio to make the changes by typing /sbin/lilo