If you want to accomplish maintenance tasks on your Derbi GP1 50 Open then it is always recommended to own a Workshop Manual to use as reference in the event you need to know techniques to take out a specific part including Brake Pads and install it again safely.
Derbi GP1 50 Open Workshop Manuals provide you with specified diagnostic information for your vehicle so if something is playing up it helps you figure out what the issue is and some ways to repair it. You will be able to determine if you can do this yourself or in case the job is just too big you could make a booking for your GP1 50 Open in with a trusted garage.
Derbi GP1 50 Open manual