Horn HI

Disconnect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
Partially peel back the front mudguard No. 1 (RH). (See FRONT MUDGUARD REMOVAL/INSTALLATION .)
Disconnect the connector.

Fig 1: Horn HI, Connector And Bolt With Torque Specification
Courtesy of MAZDA MOTORS CORP.
Remove the bolt.
Remove the horn HI.
Install in the reverse order of removal.