If you want the Win Classic type menu, do something absolutely horrifying and right click the menu button and click "Delete". Then right click the far left of the panel where it was, choose "Add to panel...", and scroll down to "MATE Menu" (or "Menu Bar" or something like that). This adds a more traditional kind of menu to it. If you want the old menu back, you can delete that menu the same way you deleted the other one, and add a "Mint Menu" to the bar. To edit the contents, right click the menu and do "Edit menu...".