How do you get the front sprocket off of a Trek 6000 mountain bike?

I'm assuming that by "front sprocket" you are referring the gears attached to the crankarms, referred to as "chainrings". If you are removing the outer two rings, use a 5mm allen wrench to remove the four chainring bolts attaching the rings to the crank. To remove the inner ring, you will have to remove the crank from the bottom bracket, a process requiring a specialized tool known as a "crank puller". For either of these processes, though, consider consulting your local bike shop to make sure you are taking the correct approach and not damaging or degrading your bike.