Turn off the light switch
Turn off the power at the breaker
Let the bulb cool down
Remove the light cover if there is one
Hold the fluorescent tube with both hands
Rotate the tube a quarter turn
Lower the tube out of the sockets
Take the old tube to be recycled or disposed of properly
Match the new tube size and type to the old one
Insert the new tube into the sockets
Rotate the tube until it locks in place
Reattach the light cover if needed
Turn the power back on
Test the light