This is pretty straight forward, but comes up from time to time. A customer called to say their screen is smaller (lower resolution) than it used to be after Windows Updates.
Notes about Terminal Server resolution:
You cannot change the resolution while in a terminal server session.
The Display tab in the RDP options before you connect is usually set to “Full Screen”. It can be set to lower resolution sizes than your current PC or Thin Client settings, but not higher.
In order to fix the problem, close the terminal server connection. Change the resolution size as needed on the local PC or Thin Client, and then reconnect to the terminal server. The new resolution settings will be passed through automatically if the display settings are still set to “Full Screen”.