Those are the (discontinued) Dicor wheel covers. They are held on by two of those chrome "nuts" on the cover. Most of them are decorative only, but the two that actually retain the covers (front and rear) have indents near the bottom of the nut, that is how you know which ones to remove. They will be 180-degrees from each other. Don't twist on the other decorative nuts!
Jayco supplied a T-wrench to remove them, but unless you are the original owner and know where it is, you will have to procure and use a 1-9/16" socket to remove them. You may need that socket anyway if a tire shop has ever worked on your rig since they tend to really tighten them down.