The front sight simply slides off, inline with the bore once it's release plunger is held depressed.
Replacement sights are also made by New England Custom Gun (use your google-fu).
The sight base, however, is sweated on - and will get waaaay out of control, should you get to trying to remove it.
FWIW, I would leave well enough alone, since it's part of the overall style/design of the rifle.
AFAIK, Burris, Leupold and most likely others (besides Ruger) make special rings that are compatible with the Ruger's receiver dovetails.
Try:
www.swfa.com
.