Turn off the main breaker
Verify the power is off with a voltage tester
Remove the panel cover
Identify the faulty breaker
Note the breaker type and amperage
Disconnect the wire from the breaker
Release the breaker from the bus bar
Remove the old breaker
Install the new breaker in the same position
Reconnect the wire securely
Snap the breaker onto the bus bar
Reinstall the panel cover
Turn the main breaker back on
Turn on the new breaker
Test the circuit
Stop and call a licensed electrician if you are unsure or uncomfortable