my e-brake is stuck on my 1999 nford mustang. how can i fix this?

You first have to find out if the handle or the cable or the caliper is holding the brake. There is not set way to go about it. I would try to get to the adjusters that are on the cable near the rear calipers on each side and there may be one under the car along the line near the brake handle. lossen them all the way and see where the cable is frosen. If it is the cable, you might get luicky and be able to remove the rear calipers and remove cable and replace. If it is the calipers, you can try using brakecleaner and a very fine emery tape to clean the piston off so it will retract or the binding may be in the mechanical acutator. If the brake handle is sticking, not too likely, then you will have to dis-assemble it and find the problem. it is a matter of removing the inside trim and taking it out by removing both top and under the car bolts.