You’re stepping into advanced authoring stage, please take a look at the Sticky: List of Useful Topics. The first few topics apply to you and read the first topic first so you understand what the menu components are.
Since your original menu is 4:3 and you’re changing to 16:9 menu with different highlight positions, it’s easier to use a menu authoring software to create the 16:9 menu for you. There will be at least 2 possible subpicture highlights: 1) wide and 2) letterbox or pan/scan. Some freewares are GFD (Gui For DVDAuthor) and DVD Styler that can do this for you. For me, I would use DVDLab Pro as it has more options to choose highlighting graphics.
Once you have the menu created, import it into DRMP using this guide: http://www.dimadsoft.com/dvdremakepro/ht_customize_menu_full.php
If you don’t like the highlight given by the authoring software and rather create your own highlight, one easy way is to use DVDSubEdit (rather than Subrip) to extract the supicture BMP as 4-bit BMP, modify it in photo editor, save it, and reimport it back into DVDSubEdit. Do this for each subpic stream (0x20, 0x21, etc.).
Last but not least, make sure the button commands (Play Movie, Scene Selections) are the same as the original menu’s.