Oh! Sorry, but you cannot do an over-the-air (OTA) update for the iOS on a jail broken iPad. You must update the jailbroken iPad using your computer and iTunes.
So, connect the iPad to iTunes, make a backup and then press the Restore button (on the main Summary tab). iTunes should then do the steps to upgrade it. Once it's done, don't put your backup on, select the set-up as new option.
Then, run the Absinthe jail break. Once it's done and your iPad is jail broken again, then you can hook the iPad back up to iTunes and select "Restore from Backup" after right clicking on the iPad (under devices). This action won't mess up your jail break, it'll just put all the apps, data and settings back on from the backup you made.
Hope this helps.
Marilyn