How do you get the stem out to replace "O" Rings?

The "stem" is called a cartridge and is replaced as a unit by Moen bat no charge. Just contact them.
In the meantime Clicking on; http://www.moen.com/consumersupport/installation/moen0133/moen0133.cfm
Will get you to a installation guide for replacing a Moen cartridge. Good luck, Tom

Great answer Tom. Indeed, you don't replace O-rings on Moen faucets. You replace whole cartridge.

( I accidentally pressed Enter button while typing your feedback message. Wanted to say: Totally agree with your answer )

As Tom suggested, you will get new replacement cartridge for free from Moen.