Loosen axle bolts. To make it easy to get the chain off, push the wheel all the way forward.
Step 2: Getting the chain off
With your left hand, push the chain to the inside of the bike. While pushing the chain, rotate the cranks with your right hang. If you have done it correctly, your chain should rest on the the inside of the sprocket.
Step 3: A helpful hint
Now that you have popped the chain off the sprocket, pull the wheel towards you. Make sure the wheel is out of the drop out to remove the chain. Remove the chain from the cog and place it in the drop out to help keep the chain from knotting up.
Step 4: The tire and the rim
Always a problem here. The best way to get the tire off is to insert tire levers under the bead of the tire at 12 and 1 o'clock. Apply pressure to pull the tire's bead out. Once you have started, follow in a circular motion around the rim until the beat is out around the whole rim.
Step 5: The old tube
At this point, press the valve stem up into the tire and pull the old tube out.
Step 6: The new tube
Place the new tube in the tire. Make sure to line up the valve stem in the valve stem hole on the rim first, before putting the rest of the tube in the tire.
Step 7: Putting the tire back on
Probably the hardest part of the whole process. In a circular motion, rotate your wrist away from you, pressing the bead of the tire inside the rim. If you need help you can use the tire levers for leverage.
Step 8: Its down hill from here!
Now you are basically putting everything back into place. Put the chain on the cog and slide the wheel into the dropouts.
Step 9: The chain
This can be scary, but don't worry it will be okay! To get the chain back on, you have to put the chain on the top of the sprocket and quickly rotate the cranks with your opposite hand.
Step 10: Tightening up!
Once you have the chain on, you must pull the wheel back and tighten the axle bolts. Make sure there is enough tension so the chain will not keep popping off.
Step 11: Pumping it up!
Now that everything is dialed in, you only need to pump the right amount of PSI (pounds per square inch) into the tire. To find this information out look on the side of the tire. After you are done, go have some fun!