@DeAnn4 There are no guidelines from Airbnb on how often (or if) cleaning/sheet and towel replacement needs to be done: discuss what makes sense with your guest and come to an agreement.
I would suggest that you may want to offer to do some cleaning and/or sheet and towel changes yourself. If the guest is dirty or doing damage to you property, it would be better to know sooner rather than later so you can do something about it, and it's an easy way to check your property over.