Most games running on SCUMM run in an aspect ratio of 4:3, a far cry from todays widescreen monitors. To compensate the SCUMMVM upscales the game untill the game's width matches that of the monitor, unfortunately this cuts off the top and bottom of the game.

To fix this, simply press ALT + Return(Enter), this will put the game in windowed mode, but the top bar is still cut off, just hover over the side of the window until you get the resizing arrows, then double-click to bring the top bar onscreen, from there if you are using Windows(I have not tested any other OS) you can drag the game by its top bar to the top of your screen and Windows will automatically resize the window to a windowed fullscreen mode, once this happens, SCUMMVM will adjust the game to fit with your monitor's height rather than width, which will result in letterboxes on the side of the screen, but no areas cut off.

Note: This process will take less time than it took you to read about this simple fix.