Place some rags under the power steering pump, remove the hose on the front side of the pump (towards the bumper.) Remove the single 10mm bolt directly below the hose nipple. Give it a tug and the nipple will be separated from the pump. The old O-ring is stuck in the pump but it can be removed with a screwdriver and clean up the surface with a rag.
If you have a leaking power steering pump, don't just replace your pump. These o-rings are more than likely the fix!! Buy this to fix that problem instead of wasting hundreds of dollars on a new pump!!