Alt + Delete in the Remote Desktop session opens the Windows menu of an application running on the remote system. The Windows menu is typically displayed under the icon in the extreme upper left corner of most Windows applications, and it lets you Maximize the application window.
You may use the following combos for sizing the window:
Maximize: ALT + Delete + x
Minimize: ALT + Delete + n
Restore: ALT + Delete + r
Resize: ALT + Delete + s