You can make changes to standard pages like the registration page by:

  1. Select Setup and go to Standard Page Center.
  2. Select customize on the page you would like to make changes.
  3. Option 1a "Select Page Wrapper" will allow you to configure the Page Wrapper.
If you have Centers enabled, you will need to be logged into the Center you want the changed to reflect, and the Pagewrapper must be available to that center.  You will also want to wait about 15 minutes or so for the cache to clear before the changes may be reflected on the live site.