The Mauser K98 was the rifle used by the Nazis during WWII, and the original rifles dating from 1936 to 1945 are considered collector's items. The K98 rifles, according to Mauser.net, are known for their reliability and accuracy and ability to shoot over 2,000 meters. The weapon was modified in a variety of ways over the course of its manufacture, and some were sold complete with scopes and bayonets while others came with adjustable iron sights. The original sights of the K98 Mauser are much like today's sights--worked into the weapon via a dovetail groove on both the front and rear. Removing the rear sight can be accomplished with basic gunsmith tools.
Ensure that the weapon is completely unloaded prior to performing any maintenance.
Position a small punch on the rear sight hinge and knock the pin out with a tap-hammer from right to left.
Depress the side "lugs" (these are two protrusions which you pinch to slide the sight up its ramp) and pull the sight toward the butt-stock.
Lift the sight up, and pull completely off the ramp.
Never point a weapon at anything that you do not intend to shoot or kill. Removing the rear sight or replacing parts on a vintage Mauser K98 from WWII will greatly decrease the value of the weapon.