This is a 5 minute task, and can be accomplished solely with the 5mm hex key included with the grinder.
The grinder ships with the lever attached to the flywheel. If you wish to remove it, start by finding a clean, stable, well lit workplace. It’s easy to drop parts and ding and dent your grinder.
Using the 5mm hex key, remove the flywheel handle from the lever. Remove the screw directly above the handle first. Remove the screw in the center of the flywheel next. Exercise caution. Once the screws are removed, the flywheel can easily become detached from the flywheel shaft. Place the flywheel lever in a safe location.