I agree. You should not change your filter material until it is literally falling apart. When you finally do change it, you need to save about 1/4-1/5 of the old material to "seed" the new material. This helps you avoid going through all the cycling stages again. It may go through a very short cycle after the change until the bacteria build up again.
Some of your beneficial bacteria will remain in the substrate so your cycle may be shorter this time than it was at first. It will still be necessary to keep on top of your vacuuming and PWC while this is happening.
BTW, unless that corydoras in the picture was cery small, your substrate gravel looks pretty big. Larger than I would normally suggest in an aquarium. Substrate of that size can easily get particles stuck down in it that can cause problems. If you've had no problems before this filter change, just make sure that you always do a very good vacuum job on your substrate.