The default display model in a KVM GUI based guest doesn't allow the screen resolution to be changed to what most would be considered acceptable. To edit the display mode run the following command:

virsh edit YOUR-VM-NAME

Scroll down to the bottom and find the video section as seen below:

    <video>
      <model type='qxl' ram='65536' vram='16384' vgamem='16384' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>

You can change the model type to any of the following:

vga, vmvga, qxl, or cirrus

In our experience qxl is great for low bandwidth connections and seems to use less processing power than the other models.