Select a unit, then press J - you will get the Go To cursor, select the target destination and all unfortified units of that type will move to the new destination. Aircraft will attempt to rebase.
Sometimes this generally useful feature can be a pain - certainly I would like the option of selecting whether my fortified units move as part of the stack or not. Additionally, if the stack move will take a number of moves to complete and you change your mind mid-journey, you have to redirect each unit individually - you cannot override one stack destination with another stack destination.