Replacing a fixed sprocket on a single speed bike requires some specialist tools. A chain-whip is used to grab the fixed sprocket so that you can unscrew it from the thread on the wheel hub. It can be difficult to remove a fixed sprocket that has been on for a long time, due to the fact that the power of the drive screws the sprocket on tighter. Although for this same reason, you can easily mount a fixed sprocket by hand. When you replace the wheel, take care to make sure you have the correct chain line and tension.
This is a long guide, so you can choose to either watch the entire video above, or follow it in smaller chunks by clicking on the individual steps below.
Steps to Replace A Fixed Sprocket:
The length of the chain can only be adjusted in increments of 1 inch(link). On a derailleur bike a spring loaded arm holds the chain in tension. If the bike has only one position for the chain the distance between the cog-wheel connected to the pedals that pulls the chain, and the cog wheel on the rear wheel that the chain pulls must be exactly right.