The Ames Suply Comapny manufactures two tools for key ring removal and replacement.  They are rather hard to find, but that’s the best way to do it.
Otherwise, I’d recommend bending the tabs up and removing the ring.  The tabs are rather hard to break, and a cap will work fine with just two tabs if you do break one.  Without the proper tools, this is the only way to remove them.  Don’t bend them too far out, just so they’re straight with the sides.  Best of luck!!