To adjust the handbrakes you need to adjust the nuts at the end of the handbrake cables, which appear through the side slots of the hand brake lever boot. Raise the back of the car and ensure that the car is stable on axle stands. Loosen the lock nuts on the cable and back the nuts off to the ends of the thread. If you haven't already done it, adjust the brakes at the wheels. Check that the rear wheels are turning freely while the hand brake is off. Now apply the hand brake four notches and go round the car to check that both rear wheels are receiving the same braking effort. At four notches the wheels should not turn at all when you try to turn them by hand, so if you can still turn them, tighten each cable adjuster nut in turn, evenly, until the brakes are on hard enough for you not to be able to turn the wheels. Nip up the locknuts and release the handbrake to check both wheels are free again. Finally, secure the locknuts. If you have just changed the hand brake cable and are having trouble, did you remember to check that the cables are the right lengh? (see replacing hand brake cables)