If you choose to do maintenance to your Kawasaki KLX250S then it is usually a great idea to have access to a Workshop Manual to keep just for a reference should you want to know the right way to take out a certain part for example the Gearbox and install it again correctly.
Kawasaki KLX250S Workshop Manuals provides distinct diagnostic guides on your vehicle so if something is playing up it will help you find out what the situation is and how to repair it. Then you are able to evaluate if this can be done on your own or in the event the job is simply too big you are able to book your KLX250S right into a decent mechanic.
Kawasaki KLX250S manual