If the window get stuck usually just loosening the 3 8mm bolts that hold the motor to the regulator will free the window.
The problem here is, as we put the windows up and down so many times the rivets that hold the regulator the door frame get loose. You can watch them move as you put the window up and down.
The rivets being able to move a little causes the whole thing to "bind" while at one extreme or another (all the way up or all the way down). As the motor weakens over time, it doesn't have the power anymore to overcome the bind and just won't move the window anymore. By loosening those 3 bolts you are unbinding the mechanism thus allowing the motor to move the window.
A new motor will fix the problem, but replacing those rivets with nuts/bolts will make the whole thing operate more smoothly.
1999 Mustang - Converted to 94 spec 5.0 EFI,
Vortech V2 SQ 12 psi, BBK shorties, Edelbrock Perf. intake,