Thank you for your question on the removal of the clutch so you can replace the sprocket.
I will give you a video that will explain and show you how to do this process.
You will need some soft rope type material to put into the cylinder to stop the rotation of the piston and will hold the crankshaft while you remove the clutch.
You will not have the tool he is using in the video, unless you order it from a web-site.
Hear is one I have found for you
Poulan/Craftsman clutch removal tool
You can do this with a large flat bladed screw driver but it is better if you use the special tool.
I hope this will help you.