The most important step is to unplug the motor. The next step is to remove the spark plug from the head. Next, unclamp the head, then pull it out of the handle. The final step is to remove the spark plug. After the spark plug is removed, you can insert the new spark plug. It's very easy to thread a chainsaw chain. Remove the old chain by pushing it through the link in the back. Then, reinsert the old chain into the sprocket on the back of the head.