Horn HI

Disconnect the negative battery terminal. (Refer to NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
Remove the front bumper. (Refer to FRONT BUMPER REMOVAL .) (Refer to FRONT BUMPER INSTALLATION .)
Disconnect the connector.

Fig 1: Identifying High Horn, Connector, Ground And Bolts With Torque Specification
Courtesy of MAZDA MOTORS CORP.
Remove the bolt (1).
Remove the ground.
Remove the bolt (2).
Remove the horn HI.
Install in the reverse order of removal.