If you wish to conduct maintenance tasks to your Honda CRF150R2 then it will always be a good plan to have access to a Workshop Manual to use as a guide if you need to know easy methods to take off a specific part like the Gearbox and fit it again properly.
Honda CRF150R2 Workshop Manuals gives you targeted diagnostic information for your car or truck so if something is playing up it will help you understand what the issue is and methods to resolve it. You can then decide if this can be done yourself or if the job is simply too big you can book your CRF150R2 in with a decent car garage.
Honda CRF150R2 manual