Medusa is equipped with a hi-flow K&N filter. This filter is made from thick cotton sandwiched between wire mesh. This type of filter is oiled to provide the best filtration capability, and it's different from foam-type aftermarket filters.
I clean mine every 10000 km or so, but if you drive on dusty roads alot, clean them more frequently.
This filter could be serviced at the place you bought the filter, or you could buy this cleaning kit for DIY Car Care. The multi-tool above is used to undo the securing screw of the airbox.
First off, undo the latches securing the airbox.
Notice the higher number of pleats on this filter. The other major difference is that this filter is 'dry', in contrast to my K&N aftermarket filter which is oiled for best filtration capability.