The same way you set it on any Linux. If you don't like the gui setting controls in look/feel, feed in boot commandline options or go into /etc/x11/xorg.conf and throw in a few likeable resolutions and restart X.
These answers are totally in the bundled notes and documentation, not to mention the Ubuntu wiki; why ask here if as if something is broken in a unique way?
Answers & Comments
The same way you set it on any Linux. If you don't like the gui setting controls in look/feel, feed in boot commandline options or go into /etc/x11/xorg.conf and throw in a few likeable resolutions and restart X.
These answers are totally in the bundled notes and documentation, not to mention the Ubuntu wiki; why ask here if as if something is broken in a unique way?