Using these replacement foams is easy. First, turn off the filter before removing the old foam. Take out the used foam and replace it with a new one from the 2 - pack. Make sure it fits snugly in the filter. For maintenance, check the foam regularly. If it looks dirty or clogged, it's time to replace it. When replacing, keep in mind that there are different styles of foam for different filtering needs, like fine and coarse. And don't forget to turn the filter back on after the replacement. Also, always store the extra foam in a dry place to keep it in good condition.