It is easy to disassemble the sight.
Assuming you have the late sight, the tension nut within the windage knob just needs to be unscrewed as far as it will go. It won't come all the way out. That nut holds the elevation knob shaft. If you have the cross bar sight, unscrew the cross bar (watch for a spring under the cross bar). Push the elevation knob shaft from right to left. Unscrew the windage knob. Use your thumb to push up on the rear sight aperature. This will pop off the rear sight cover. Clean as needed. Oil when done. You don't need grease here, this is not a heavy wear area.
Reassemble.