First, make sure you have the most current version of iTunes. Then, plug in your iPad and open iTunes. On the main summary page is a button where you can check for updates. Press the button and iTunes should tell you that there is an update available. It will ask you if you wish to upgrade. Accept the option to upgrade and then let iTunes do the work. After some input from you (prompted by iTunes)m you should be on iOS 6.
Oh, and do a backup before you do the update. You probably won't need it, but it never hurts to be prepared. Good luck.
Marilyn