It will be difficult (or even impossible) to edit the actual menu but it is quite easy to remove it and replace it with something you much prefer by a process called re-authoring
You will need a dvd authoring software such as Ulead Movie Factory 4 or MovieWorkshop2
Consider the DVD to be a collection of video files ( called vob in a dvd) with an index ( or table of contents) linked to the menu. "chapters" are defined and navigation to them in this index.
In removing the menu, you are getting rid of the "table of contents" and replacing it with your own specifying the new name , background image : Still or motion, and any music.
Depending on the program you use you may also be able to say how you want each button in the menu to behave. and you can rearrange the order of play
I recently used both programs to re create a DVD with menu from a dvd (+RW) recorded on a settop dvd recorder from vhs tape
try these links there are free trial downloads
http://www.ulead.co.uk/dmf/runme.htm

http://www.ulead.co.uk/dws/runme.htm

There are of course other programs but I find these easy to use affordable and stable. ( .. no..I dont work for ULead!)