IF you not yet removed the existing wheel and it is not dried out, place the old wheel in your tank when you replace it. Also there will be bacteria on your filter pad if it has been in your filter for more than a few days. Do not replace the filter for a couple of weeks while your wheel gathers its bacteria. Watch your water quality for awhile.
How long have you had your filter with the bio wheel? I know people who have had them for years and never had to replace them, Ive never even heard of them falling apart. When they have a good amount of bio bugs living on it it does start to look pretty nasty but thats a good thing.