First off you will have to remove your airbox, its secured down by 2 rubber stoppers at the top and a rubber plug at the bottom
it should just pull to remove.
Next take the airbox apart its just a case of uncliping it and removing the filter from inside.
Its always best to drill the holes on the left side of the airbox (the side that will be furthest away from the engine) so it dosnt suck up all the grit and hot air from inside your engine bay.
best bet to use a spade type drill bit like
as drilling lots of little holes wont sound as good as a few bit holes.
make sure you drill ALL the holes below where the filter sits or you will end up sucking in unfilterd air in to your engine, which will ultimatly wreak it!
once done with the drilling give it a good clean then re-assemble the airbox.
put the filter back in clip the lid back on.
now refit the airbox sit it back in the 2 top rubber mounts and pull the lower plug back through the hole make sure its all clipped together properly.
and your done!
take if for a drive see if it sounds any better
for better results id reccomend a green cotton pannel filter
http://www.green-filter.co.uk/