If you want to carry out adjustments on your own Aprilia ETX 350 AE then it is usually a good idea to have a Workshop Manual to keep just for a guide if you want to know how you can strip off a particular component for instance the Brake Discs and fit it again properly.
Aprilia ETX 350 AE Workshop Manuals will give you special diagnostic guides for the vehicle so if something is faulty it can help you find out what the problem is and some ways to fix it. Then you are able to evaluate if you can do this by yourself or in the event the job is simply too big you can book your ETX 350 AE into a decent repair garage.
Aprilia ETX 350 AE manual