Find the valve, make sure the tube is fully deflated and remove the lock-ring (if any).
Unseat the bike tyre
Pinch the bike tyre to unstick it from the rim and let the bead fall into the well of the rim.
Bike tyre Levers
tyre levers have two hooks. Across one end is a hook to go under the bike tyre bead. Near the other end is a notch to hook onto a spoke. Metal levers last for ever but may damage fancy rims if used carelessly. Plastic levers tend to break, keep your hands over them when levering so that if they do break nothing will fly off and hit you in the eye.
Repeat the previous step moving the lever a few millimetres each time. Take care to keep the active lever under the bead. If it pops out you may have to start again.