Gather a tire lever, a pump, and a replacement tube
Remove the wheel from the bike
Deflate the tire completely if it is not already flat
Pry one side of the tire bead off the rim using a tire lever
Pull the old tube out of the tire
Inspect the tire and rim for thorns, glass, or sharp debris
Check the rim tape for damage or misalignment
Lightly inflate the new tube just enough to give it shape
Insert the valve through the valve hole in the rim
Tuck the rest of the tube into the tire
Push the tire bead back onto the rim by hand
Use tire levers only if needed, and avoid pinching the tube
Make sure the tube is not trapped between the tire and rim
Inflate the tire to the recommended pressure
Check that the tire bead is seated evenly all the way around
Reinstall the wheel on the bike
Spin the wheel and check for wobble or rubbing