Can i clean fish tank filters or do they have to be replaced and how?

I'm not familiar with your filter but if you are talking about the filter cartridge then yes it needs to be replaced. After about 6 weeks carbon becomes used up and can not absorb any more of the bad chemicals that you want out of your tank which is why you run carbon in the first place. Keeping the carbon after it has been used only leaches bad stuff into your tank. Good bacteria will build up in the actual filter housing area itself as well as in your tanks gravel, so replacing the filter cartridge will not remove all the good bacteria nor will it start another cycle. Some things like filter floss it is best to rinse off in the water you remove from your tank during a water change. Put that water in a bucket and squeeze all of you sponges and filter floss in the water until they run almost clear. This removed debris and anything else but keep good bacteria. Honestly in the long run the best best is a canister filter. I recommend a fluval 305 (or a smaller or larger model depending on the size of your tank).

Freshwaters easy, I've never had a problem keeping freshwater tanks and never lost a fish. I'm currently maintaining a 2 year old, established reef tank and am doing great.

You dont need to replace the cartidge unless it is falling apart or beyond cleanable.

You are right about the charcoal, you only really need fresh charcoal to remove medications from the water.

Most of the bacteria cycling the tank live in the filter. Some of that will stay in the biowheels and keep the cycle safe. But I still suggest you only rinse the cartridges now and the, maybe once a month depending on your fish and how dirty they get. You should only rinse one , then wait at least a week to rinse the other one. unless you rinse them in a bucket of tank water or dechlorinated tap water. You can add extra bio material to the filter, to hold more bacteria, evan a chemical free sponge helps.

If your tank is cycled, replacing the filters is a big no. That's where most of the bacteria live that cycle your tank! You can't just throw that stuff away!

You'll need to rinse it in a bucket of tank water. Not in the sink because that can kill the bacteria because of the chlorine in the water. Only replace the filter when it is falling apart.

I'm not familiar with that filter, but generally sponges and bio media should just be rinsed in old aquarium water when they get too gunked up so you don't kill any beneficial bacteria which is mostly found in your filter, carbon needs to replace every month or two if you even want to run it.

Rinse them! Starting over means cycling all over. Most folks who replace were told to by the people at the store. But you really shouldn't have to. Just rinse them well and put it all back together