Click the button in the upper left corner of the title bar and select Restore
Or click the 
button
Or right-click the window title bar and then click Restore
Or press ALT+SPACEBAR+R (application) / ALT+HYPHEN+R (document)
Restore restores the active application window or document window to the size and location before the Maximize or the Minimize command was used.
To restore the window:
Click the button in the upper left corner of the title bar and select Restore
Or click the button
Or right-click the window title bar and then click Restore
Or press ALT+SPACEBAR+R (application) / ALT+HYPHEN+R (document)