You'll always need to use the brakes on a Metro when going down hill. Just make sure the brakes have been adjusted.
You can tighten the brakes by adjusting the wing nuts on the brake linkage down. Depending upon what model you have and when it was built will change the manner you use to check the adjustment.
If you unit has a parking brake built into the thumb latches (pistol grip or ECS) you simply want to tighten the wing nut until the park brake locks the drive wheels in place. If you have an older Metro you'll want to tighten the wing nut until there is an 1/8" gap between the drive lever and the handle bar grip when you squeeze the drive lever.
Give me a call at 800-667-5296 if you have any questions. It's often easier to explain over the phone.