here is a guide to fitting a new horn on a facelift Auris 13 plate
remove 2 clips and 1 bolt from grill
put your hands into bottom of grill and gently pull forward to unclip the grill
clips are arrowed in picture.
image with grill removed,remove upper cover to give better access and unbolt
the horn.
new horns are now fitted.
re-assemble in reverse.