Welcome to AA!
First, read up on cycling with fish here on AA. It's crucial to understand the nitrogen cycle if you want a healthy aquarium.
Second, never replace the filter media unless it's falling apart with the exception of carbon.
You'll just have to wring out the sponge in a bucket of old tank water once or twice a month. I've been running the same sponges in my AquaClears for more than a year.
The carbon does get plugged up, but I don't run it unless I'm trying to remove medication or tannins from the water, which is rare.
The biomax is just very porous ceramic that provides a lot of surface area for beneficial bacteria colonies. No need to replace that either.
When you replace the filter media, you lose your nitrifying bacteria, causing your tank to cycle and, possibly, fish deaths.