First the filter, to get the easy issue out of the way
Carbon gives out as it adsorbs [I mean adsorb, not absorb] "stuff" from the water. The time depends upon what it is adsorbing. In a very lightly stocked aquarium with good water it could last a few weeks, whereas in more heavily-stocked aquaria or those with "stuff" in the water it can last only a week or two. Personally, I never use carbon. But I have planted tanks, and as carbon removes nutrients along with "stuff" and the plants remove the "stuff" anyway, it is not good for planted tanks. Many members suggest keeping it on hand for removing medications if that becomes necessary.
The other filter media like the pads should not be replaced until they no longer function properly. Rinse them as needed to keep them from clogging. This slows the water flow, and partially defeats their purpose. Once the pads/floss/wool becomes so ragged that it literally falls apart or the water is able to get around it rather than going through it, it is time to replace it.
Now the big subject, water changes. The type of aquarium, number of fish and type of fish, and plants or no plants determine the extent of water changes. The more plants and fewer fish (with plants), the less water changes are required. But the more fish, or larger fish, the more they are necessary (planted or not).
A weekly partial water change is the best overall schedule. We had a couple threads on this recently you might search for, and there was a series of 2 articles in the November and December 2009 issues of TFH that went into this subject in minute detail. I won't go into all that, other than to repeat than a weekly water change is recommended if one is needed by the fish, etc. as mentioned above.
The volume also depends upon the fish load, but I always suggest 40-50%. I have heavily-planted tanks (check the photos under my Aquariums) but I still do a 50% water change every week without fail, and have for 15 years. I have a lot of fish in my tanks, and it is needed. Changing water is the only way to effectively remove "stuff" in the water that filters cannot remove; plants can but again this means a light fish load to balance. Most of us like more fish than that, so a weekly water change is a good idea.
Last thought; there are products in the market [made by reputable firms no less] that claim to reduce or eliminate the need for water changes. These are not good. They interfere with the natural bacteria in an aquarium, and I do not believe that is advisable. Nature has its way of handling things, and as an aquarist I prefer to assist it with water changes (as would occur in nature) rather than adding chemicals and whatever that is going to create excess ammonia and influence the bacteria colony. The claims as towhat these products will supposedly do approaches the unimaginable.