If you wish to edit an existing menu, you may wish follow the instructions in Extracting a Menu Page to print out the menu first. Study the menu options and structure before you make any changes.
Follow the procedure Selecting a Menu Page to select a menu to edit.
The Map Editor's editing screen is displayed. This will look rather different depending on whether you are using a 4.5xx or 4.6xx release of DP4.
Editing 4.6xx DP4 Menu pages is described here.