Removing a tire
To remove the rear tire from your motorboard use an adjustable wrench to remove the nut from the wheel axle bolt. Once the wheel axle bolt is removed, the tire will be free.
To remove the front tire, an appropriate allen wrench is required.
In both cases, when replacing the wheel, make sure the bolts are tightened fairly strongly by hand. Be careful not to tighten so tight as to cause damage to the bolts, but enough that vibration will not cause them become loose.