Full screen is Ctrl+Alt+Enter, not hard to find out so I assume you want the full resolution?
Go to finder, click on your HD, go to Library>Preferences>System Configuration
Copy the file "com.apple.Boot(.plist)" to your desktop, open it.
Create a new line after <dict> and before </dict>
Type (or copy) <key>Graphics Mode</key
<string>1280x1024x32</string>
Obviously, if the resolution you want is 1920 x 1080 you'd type <string>1920x1280x32</string>
Save that file, and copy it into Library>Preferences>System Configuration
Reboot the VM and that *should* be it sorted.
