Cam Timing

I've got a 2006 TRX 250 EX which has some issues. I've throughly cleaned the carb and am still having engine stalling at low rpm. It will start with the choke on but needs reved continuously to keep it going. The engine backfires and doesn't rev as it should at higher rpm. The air box and K&N are clean. It seems similar to a mistimed cam. My belief is my rev happy daughter has jumped the timing while stuck in the mud. I'll need some info as to pulling the engine apart to replace the cam chain and look for possible other damage. The engine sounds fine mechanically and doesn't smoke. I plan on checking the valve clearance first and do a compression check before getting serious. I have the tech data for checking the timing and valves but will need info pretaining to replacing the cam chain and maybe pulling the head. Thanks