That silver cap probably _has_ to be removed. The wheel bearing nut is under that, secured by a cotter key. Be sure to repack the inner and outer wheel bearings while you have it apart. Get the shop that turns the rotors to do it, using a grease packing tool. Doing it by hand is messy and not as effective.
On one of my old vehicles it was possible to remove the rotors by unbolting the spindle bearings. I'll bet you aren't that lucky.
Tom S