All right... for this first trek into the world of ResEdit I'm going to go really slow and use a lot of pictures; after this we'll speed up a little. Remember, now -- the stuff you are seeing here as far as opening the resource (MENU in this case), changing it's contents, saving, etc. applies to a large portion of the rest of how ResEdit works.
Click on the button #4 to the right to see another screen dump. You sharp people out there may know that menu ID#'s (normally) start at 1, that being the Desk Accessories menu. Since that one's sorta boring, I skipped it to go to the File menu for our little session instead. What we see here is the first item of information for MENU #2, namely, the title that you normally see on the menu bar. All the stuff you see at the top of the illustration, menuID, width, height, all the way to enableFlgs, I leave alone. I think that leaving width and height at zero lets the Mac figure our automatically how to scale the menu as you make other changes, but I'm really guessing. The thing we want to change here is the title, which currently is good 'ol File. Asterisks denote where the information for one item ends and another item's info begins.