Locate the skewer on the center of the wheel attached to the bicycle frame slots.

Turn the skewer lever away from the bicycle.

Turn the skewer cap counter clockwise.

Once it is loose enough, you can pull the tire off, but do not pull it yet entirely off.

If your bike does not have a quick release for the wheel, you will need to unscrew the axle nut.

Some anti-theft gravity nuts require the bike to be upside down, others need a special wrench. However, you'll know if you have bought such an anti-theft device.