Is it best to update from my computer or can I just update from my ipad over wifi?
You can NEVER update a jailbroken device, either using iTunes or Wifi.
You must use the "restore" feature of iTunes if you want to update the version of IOS on your device.
Before you do that, you should take a full backup of the device (iTunes or iCloud), and ALSO make a decision about what jailbreak apps / tweaks you may want to backup and restore. To backup JB tweaks etc. you can use an app from Cydia such as PkgBackup or xBackup. Or you could simply write them down and reinstall them again. The best approach will depend on the complexity of your jailbreak.
Once you have used iTunes to restore the device to 6.1.2, then you restore your iPad backup, re-jailbreak, and then (optionally) restore any tweaks which you backed up separately.
If I get some spare time tonight I'll update our old tutorial on upgrading a JB device -
http://www.ipadforums.net/jailbreak...des/26399-how-upgrade-your-ios-jailbreak.html, however the principles are exactly the same. You can simply ignore all stuff about sn0wbreeze as it would now be an evasi0n jailbreak (that's the piece I'll update later).