I don't know if you still need help but I'm posting this to help anyone else who has this problem.
What bebop460 wrote would work:
3 Another option is the software utility that comes with a graphics card. You can also go in there and set the resolution or resize the desktop to your liking.
I have a nVidia graphics card and all I needed to do to change the screen size itself was go in the graphics card settings, go to 'Adjust desktop size and position' and change perform scaling. 'GPU' scales the screen from the graphics card and 'Display' scales the screen to the monitor size.
This literally took me about 5 minutes to figure out, if you have a different graphics card, go to your graphics cards settings and have a little play round, there should be a 'Return to Defaults' button somewhere if things go a bit wrong.
IF you still need any more help I would recommend going to your graphics card manufacturers website and contact the help line from there.