How do you you adjust the additional external monitor display to use entire monitor screen?

Depends on the operating system:

XP: Right click desktop, click Properties. Then click on Settings tab. You'll be able to adjust resolution from here.

Windows 7: Right click desktop, click on Personalize. Then click on Display (bottom left, where it says 'See Also'. On the top left you'll see a link that says Adjust Resolution. Click this and you'll be able to adjust resolution from here.

If you've got a different operating system, let us know and we'll give you the instructions.