Turn off the light switch
Turn off the power at the breaker if possible
Let the tube cool down
Use a stable ladder if needed
Hold the tube with both hands
Rotate the tube a quarter turn until the pins align with the slots
Lower one end of the tube out of the fixture
Remove the other end of the tube
Check the new tube type and size match the old one
Insert the new tube pins into the slots
Rotate the tube a quarter turn until it locks in place
Restore power
Turn on the light to test it
Dispose of the old tube properly