This is a instructable on how to change the front sprocket on a Yamaha Raptor 700. The tools you will need are:
-ratchet or impact gun to fit socket
The first step is to take off the sprocket cover. It is held on by 2-5mm allen screws.
After removing the sprocket cover, the sprocket nut is exposed. As you can see there is a lock washer that holds the sprocket nut in place. In order to remove the nut, you must pry back this washer to undo the nut. I used the screwdriver and hammer to get under it to bend it back up. Be careful to not bend the tab on the washer too much or else it can break off.
Once the tab on the washer is bent back, you can get the socket onto it. You can either use a impact gun or a ratchet to get the nut off. An impact gun makes it easier and less strain on the transmission. Make sure you have the atv in gear or else the sprocket will just spin and wont be able to break the nut loose.
When the nut is off, you are left with the sprocket with the chain around it. At this point you can pull the sprocket straight off of the shaft. Once it is off then you can change to a different sized sprocket for whatever power you would like to have, whether you want more low end or top end will determine the size of sprocket you go. To put the new sprocket on, you will need to loosen the chain. You take the sprocket and line it up with the splines on the shaft. It should slide on pretty easily. Then when you have it on you can wrap your chain back around it. Tighten your chain to your preferences, then repeat the steps in reverse order. Make sure you put the lock washer on before you put the nut on and tighten it down. Pound the tab back down onto the flat side of the nut. There is two tabs, choose the one that will best line up with a flat side of the nut. Replace the sprocket cover and you are finished.