depends what it is, make, model, year, engine size??? some can only be done at the bike shop electronically, others you can do yourself by removing restrictive devices from the carb, exhaust pipe, variator and/or changing the CDI. You might get a more detailed answer if you re-post in the Motorcycles section with machine details!
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix vans.