If you want to perform adjustments on your own Yamaha DT50X then it is always a great idea to own a Workshop Manual to use as reference in the event you need to know methods to remove a specific component much like the Brake Discs and match it again in the right way.
Yamaha DT50X Workshop Manuals can offer you particular diagnostic info with regards to your vehicle so if something is broken it will help you ascertain what the problem is and the best way to correct it. After that you can analyse if this can be done by yourself or if the job is simply too big you can book your DT50X right into a nearby mechanic.
Yamaha DT50X manual