I changed the display size to 1600x1000, but on every login it changes back to the maximum setting of 1920x1440, so I have to change it back again. I normally only need to do that once or twice per day, but it's becoming a bit of a nuisance. Any solutions, thanks guys.

in System Settings -> Hardware -> Display and Monitor -> Display Settings, change your resolution and Save this specific display arrangement. Then make sure you save the Session on logout (also in System Settings: Workspace -> Startup and Shutdown -> Desktop Session