Search is your friend. Some one posted the steps:
You simply remove the plastic cover piece that is over the radiator/hood latch area by removing the 8 plastic pin fasteners (use a screwdriver to pry the center posts up in each fastener then the fasteners will pull right out).
Unscrew the bolts holding each of the two original horns in place, disconnect each horn's wires by unplugging them from the wire sockets (it will be obvious).
Then bolt the replacement horns in as shown in my picture (they mount through two of the holes previously used with the plastic pin fasteners that hold the cover on.
Plug the wire adaptors that come with the upgrade kit into the wire sockets and then connect each to the horn terminals (slide on connectors). Test the horns.
Reinstall the plastic cover using 6 of the 8 fasteners you removed when taking it off. Take your time and it shouldn't take more than 30 minutes or so.