the carbon pad if you used it must be removed and discarded within 30 days. as far as the rest of the media the pads should be washed clean in tap water, the bottom layer (pasta) can be washed clean in tap as well. the roundish pebbles (ehfisubstrat) in the middle are your biomedia so you should rinse off only 1/2 of it at the most in tank water in a bucket. then put everything back together. The impeller and impeller well can be washed with water and rubbed clean also.
When you turn the filter off (unplug it), you then turn the valves to stop flow, take the filter away to your sink, open both valves, tip it to pour the water out, then open it.
Then to put it back, let the water out of the "OUT" hose to your tank (make sure the spraybar is out of the water when you do this so it sucks air) into a bucket.
Then put everything back together and open the valves. the canister should refill. once its full plug in. should work fine.
You should only need to do this every 3 to 6 months. If you have a lot of mechanical filtration on your tank (I run one with a couple of large Aquaclears full of foam) you may need to clean it less frequently. My eheim only never really gets very clogged because theres no debris for it to suck up so I almost never service it.