Also, you can press Alt+Spacebar to get the program's context menu (similar to clicking on the icon in the upper-right of the window.
Then pressing left & right will go through the entire program's menus, but (depending on the program) can also go to the individual worksheet's context menu. If you get there you can then go down to "resize", which will give you the 4-arrows resize icon for the worksheet itself (not the main program window). Then press the down key, and the right key (which will let you resize the lower-right corner). Then use the mouse to resize the worksheet.
Then press enter (or click the left button) to finish resizing. This helps with windows are larger than the screen and you're unable to resize them.
Finally, go back to the original author, and swap their incredibly huge high-res screen with a more sane one. You'll never have this problem again :)