Lower the door and dismantle it by removing the hardware. Lower a double door by recruiting at least two helpers to help with the weight, and place a 2×4 block under the door to prevent smashing a foot or finger when it’s lowered. Remove the sections one at a time by disconnecting the rollers and brackets. If you have windows, tape them to help control flying shards if they break. Then remove the old roller tracks and remaining hardware.
The electronics should also be inspected before or after investing in the cost of replacing the garage door panel to make sure your door will operate properly. The sensors prevent the door from closing on someone's foot or a pet. If they don't work, someone could be injured. Also check to make sure the door opener works, since you could otherwise be locked out of your garage.