Bike tubes are sensitive things. Even with a protective rubber tire over them, sharp objects can penetrate your treads and puncture the tube. This can occur very sudden and take your bike out of commission. Most long-distance riders carry a spare tube--sometimes two--with them when riding their bicycle. If you have to change out your bike tube, one of the toughest aspects of the procedure will be removing the tire from the rim.
The common way to remove a bike tire is to start by taking off the valve cap. On the side opposite the valve, place a tire lever beneath the edge of the tire, known as the bead. Pull down to try and pry the tire up off the bead. You might also try to latch onto a spoke, providing more leverage. Take another tire lever and place it 6 inches to the side of the first one, and pry up on this location as well. Repeat this with a third lever so that the tire pops off the rim.
Some cyclists choose to remove only half the tire in order to access the tube and remove it. This makes reinstalling the tire on the rim much easier. You can do this by stopping once part of the tire is removed, then pulling out the tube. However, you are less likely to identify what caused the tube to break when using this method.
Another way to remove the tire is by using only your hands. For this method, squeeze the sides of the tire on the side opposite of the valve--this forces the beads into the rim well. Then, pull one side of the tire up and over the side of the rim, creating a small opening. Once you do this, you can go along the rim, bringing the rest of the tire slowly over the rim and creating space to remove the old tube and install a new one.