KTR sell a cleaning kit for their filter -->
http://www.k-tecracing.com/show_product.asp?id=4778
Foam filters are fairly straightforward to clean, they have quite a high dust/dirt holding capacity though so unless it looks particularly dirty I wouldn't worry and leave it another year.
But if you've a free weekend and fancy cleaning it why not, it won't do any harm.
No doubt the cleaning kit from KTR will come with instructions but usually foam filters it's something like:
-Knock out any large particles by hand gently tapping the filter.
-Rinse the filter out with cold water from the clean to the dirty side, a small shower head is particularly useful for this as you can stick it inside the neck and the flow helps flush some of the crap out.
-Soak the filter in the cleaning kit 'filter cleaner' solution and allow it to penetrate for a good 5-10 minutes, this mainly brakes down the old filter oil and any remaining fine dust/dirt.
-Thoroughly rinse the filter again ensuring all the cleaner solution comes out.
-Let the filter dry, you can speed up the process with a hairdryer but go steady with the heat setting as you don't want to start breaking down the glue that holds the foam together.
-Once the filter is completely dry re-oil the filter according to the instructions, you don't need loads of oil so don't overdo it. Putting too much on can impede the airflow.
