Turn filter off at power point and unplug it.
Lift intake hose out of aquarium and put it in a bucket. Have intake strainer at bottom of bucket otherwise you get a face full of water.
Lift outlet hose out of tank and put in bucket.
Gently lift filter up above bucket and some water should come out.
When water stops coming out of the filter, grab the inlet & outlet hoses, and filter case and carry them outside or into the bathroom, laundry, wherever you plan on cleaning it.
When you are outside, undo the clips holding the lid down and remove the lid.
Tip water out and remove filter media. Put media in a bucket of tank water and squeeze it out. When it's clean put it in another bucket of tank water until the filter case has been cleaned.
The filter case, the inside of the motor, the impellor assembly (magnet with 3 or 4 plastic blades on one end), and the hoses can be washed under tap water.
There might/ should be a round plastic disc on top of the impellor assembly and this should be removed to gain access to the impellor.
Be careful with the impellor assembly. It should have a rubber grommet and possibly a plastic washer on each end of the impellor shaft.
The impellor shaft is either stainless steel or ceramic. The ceramic shafts can break so handle with care and don't be rough with it.
The rubber grommets come off each end and so do any washers. The impellor should then slide off the impellor shaft. Clean all these bits under tap water but don't lose the little bits down the drain. I wash them in a sieve for sieving flour.
Wipe out the inside of the motor when the impellor assembly goes. You can use a tissue or paper towel or your finger. Just try to remove any gunk from in there.
Flush water down the hoses.
When everything is clean, reassemble the unit and carry it back to the fish tank.
Put the intake and outlet hoses back on the filter (assuming you haven't already), and put the intake tube back in the tank.
Take the outlet hose that normally goes in the tank, and suck on the end of it for a few seconds to get water draining into the filter.
Put the end of the outlet hose into a bucket and let the filter fill up. When the filter is full and water is starting to flow into the bucket, put your finger over the end of the outlet hose, lift the hose up and put it in the tank. Clip the outlet/ return hose into the suction cups or whatever is holding it in place.
Dry your hands.
Plug the filter in and turn it on. Let it run for a minute and give it a gentle rock from side to side, just a couple of times to dislodge any air bubbles.
Check the filter for leaks and you are done.