You see that cap in the center of the rotor?  Remove it, underneath
you will find a large nut that is probably held in place by a detent
in a washer.  You can gently straiten the detent out or just unscrew
the nut with the appropriate size socket wrench.  Make sure to repack
the bearings when you are putting it back together.  A Chiltons repair
book is a really handy thing to have.

                      ...Ron
--
68' Camaro RS
88' Firebird Formula
00' Mustang GT Vert

The Elantra uses captive rotors that are held in place primarily by the
wheels, but there are two visible screws that hold the rotor to the hub
when the wheel is off. You need to remove them first, then knock the
rotor off from behind. They can become rusted in place, so considerable
effort may be needed to get it off. Be careful about pounding on it too
hard with a hammer, as you can crack or damage the rotor. Use a rubber
mallet or a block of wood and a hammer.

The 01 Elantra rotors "slide" off and on.  I use quotation marks because
rust buildup often makes it nearly impossible to remove the rotor.  There
are two #3 Phillips screws which retain the rotor in place.  You'll need
to remove them.  I recommend against attempting to pull the rotor off by
using the threaded holes in the rotors.  Nearly every time I've done this,
I've cracked the rotor.  I have a 3.5Lb plastic hammer I use to try to beat
them off.

My recommendation is to try to remove the stud without removing the rotor
if you can.