Some times its very irritating to work on Full size Remote Desktop Windows, i tried below solution and it worked in changing the screen size instantly.

To open Remote Desktop Connection, click Start, point to Programs or All Programs, point to Accessories, point to Communications, and then click Remote Desktop Connection.

When you click Connect, the information you have entered in Options becomes the default setting for all Remote Desktop connections and is saved in a file called Default.rdp

  • To change the screen size for connections
  • In the Remote Desktop Connection window, click Options.
  • On the Display tab, under Remote desktop size, drag the slider to choose the size of your remote desktop. Drag the slider all the way to the right for full screen.
  • Click Connect.