How to replace a flat innertube

Remove the flat wheel from the bike.
Start by undoing the brake if you don't have disc brakes, then undo the quick release. If it’s the front wheel unwind the quick release. If it’s the back wheel shift the chain into the hardest gear (smallest sprocket). Then pull the derailleur back so the sprocket does not hit the jockey wheel.

Take the valve caps and any lock rings off your tire. Take the first tire level and insert it in on the opposite end of the tire as the valve. Place the tire lever under the bead of the tire (the part that sits behind the rim).  Take the second tire level and insert it 12 cm down on the same side that you inserted the first lever.

Lever the first tire lever and then lever the second one. The tire should pop over the rim freeing up enough slack to peel the tire off the wheel with your hand. Do not take the tire completely off of the wheel.  Take the old tube out.

Mechanics tip: If you have a puncture check the inside of the tire with your fingers to make sure the debris that has punctured your tire is been removed.

Partially inflate the new inner tube and place the valve of the inner tube into the hole in the rim of the wheel. Push the rest of the tube into the rim starting at the valve hole and working your way round the wheel. Place your wheel on the ground with the valve hole on the top and the uninterested bead of the tire facing away from you. Starting from the top of the tire push the bead back into the rim on both sides slowly working your way down the tire.  Gently place your tire lever under the last remaining tire bead sticking out, slowly levering it back up. You may need to do this a few times to insert all the remaining tire bead into the rim.

Mechanics tip: At this stage is it easy to pinch the inner tube with the tire bead. Be careful and work slowly.

Inflate the new tube and replace any valve caps or locking rings. Reattach the wheel to the bike.