Turn off the main power supply
Verify the circuit is de-energized with a voltage tester
Remove the panel cover
Identify the faulty breaker
Disconnect the wire from the breaker
Release the breaker from the panel
Install the new breaker of the same type and rating
Reconnect the wire securely
Snap the breaker into place
Reinstall the panel cover
Turn the main power back on
Test the new breaker by switching it on and checking the circuit