Turn off power to the bathroom fan at the breaker
Verify the power is off with a voltage tester
Remove the fan cover
Remove the fan motor and housing screws
Disconnect the wiring from the old fan
Remove the old fan unit from the ceiling
Check the opening size and duct connection
Install the new fan housing or replacement unit
Connect the wiring to the new fan
Secure the fan to the ceiling framing
Reattach the duct to the fan outlet
Install the fan motor and grille cover
Restore power at the breaker
Test the fan operation
Seal any gaps around the housing if needed