If you have a filter, because the water is always flowing across the filter media, that is where the highest concentration of beneficial are going to grow/live. In a fully cycled tank, the beneficial bacteria will live everywhere in the tank... on the glass, in the water column, on decorations. But the concentrations of the bacteria will be so low in these other places that it doesn't mater if you replace/wash these items and kill off that bacteria. It's the colony in the filter media you want to protect.
You don't say if you are doing a fishless cycle or a fish-in cycle. Either way, you need to get a set of liquid test kits (like the API) for ammonia, nitrite, and nitrate.
If you are doing a fishless cycle, then there is no need to change the water. You simply want to dose the water with pure ammonia (Ace Hardware brand used to be one that didn't add soaps to the store brand ammonia) until you get an ammonia reading of about 4ppm. Then simply let the tank sit with the filter running testing ammonia levels daily. Eventually (like after about a week), the ammonia levels will start to drop because the 1st type of bacteria will have colonized the filter converting ammonia to nitrite. That is when you will want to begin regularly adding ammonia to the tank to maintain ammonia levels and start testing for nitrate. When nitrate levels start going down, start testing for nitrate. When nitrates get really high, do partial water changes. When you can dose the tank with enough ammonia to raise levels to 4ppm, and in 24 hours have zero ammonia and nitrite levels, your tank is cycled and ready to add fish.
If you are doing a fish-in cycle, then you need to test daily and do partial water changes to keep ammonia and nitrite levels no higher than about 1ppm and nitrate levels no higher than about 20ppm. Your tank will be cycled when you no longer have to do partial water changes to keep ammonia and nitrite levels in check. Then you can continue testing for nitrate until you learn how often you need to do partial water changes to keep nitrate levels in check.
When you do partial water changes, rinse your filter media to get junk out of it... but ONLY rinse it with 'old' water from your fish tank. NEVER rinse it with tap water. The chlorine in tap water will kill the bacteria you just finished growing.
A well established colony of beneficial bacteria will quickly reproduce, so if you do need to change the filter media, you are always fine to change 1/2 the media. The old 1/2 left will quickly multiply and start growing on the new media.
Some filters today are now designed that you have a filter media that you change regularly to remove particals from the water, and another section designed to grow the beneficial bacteria. The section designed to grow beneficial bacteria doesn't need to be any kind of filter material, just something with lots of surface area for bacteria to grow. If gunk accumulates of the material you don't change, make sure to only rinse it in old tank water.
