Do you want the Hexlox 5mm in black - or silver? Other than that you're done. Simply replace your current bolt, Insert the Hexlox 5mm to block access to the bolt. The Hexlox Key "locks and unlocks" the bolt.

Don't forget that you need to protect both the saddle and the seat post. Even if the saddle is secured a thief could easily remove the seat post - with the saddle.