If you mean Seachem Matrix (rocks), only once did I a rinse it off with tank water. I run a filter sock before it, so there really wasn't really anything to rinse off. I have not touched it since.
Like the above post says, you don't replace it -- it is just a home for de-Nitrifying bacteria to live much the same as live-rock.
If you mean the Matrix Carbon packs, then I think they have a life of 1-2 months then you should replace them.