changing screen size wow

I'm trying to change the size of each screen on the game wow to help with lag. when i go to the system tab to change the size of each screen it won't let me change it.

[MiRai]

Your Window Layout dictates what resolution each game client is going to render at. So, you can either:

1) Pick a new Window Layout (with a smaller Region 1)
2) Use the 3D Render feature to render your game clients at a smaller resolution while maintaining the size of your regions
3) Disable "Instant Swapping" in your Window Layout (you will lose the ability to use 1:1 mouse broadcasting)