If you want to undertake maintenance tasks on your own Derbi Supermotard Racer then it will always be recommended to have access to a Workshop Manual for a reference in the event you want to know proven methods to remove a specific component including Gearbox and install it again accordingly.
Derbi Supermotard Racer Workshop Manuals will provide you with specific diagnostic info with regards to your automobile so if something is broken it helps you ascertain what the issue is and tips on how to resolve it. You will be able to analyse if this can be done yourself or that the job is simply too big you can still book your Supermotard Racer right into a local repair garage.
Derbi Supermotard Racer manual