[ubuntu] How to adjust screen resolution?

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http://ubuntuforums.org – I try to follow http://www.howtogeek.com/howto/14434...buntu-live-cd/ to do a virus scan. When I get to the last bit where I want to start the scan, the "Start" scan button is out of reach. It is well below the bottom of the screen. I can't move the dialog upwards or re-size it so that I can get to the button to click it. Nevertheless I can't find anywhere I can re-define the screen resolution so that I can get to the button. It is a surprise to me that the screen resolution cannot be adjusted. Please tell me what I have missed! I run the ubuntu 9.04 Desktop Edition as a live (Hardware)