Updating to iOS 9.2.1 requires at least 610 MB of free space on your iPad. Please change your media sync options to make more storage available.

Do you have a question ? Your current free space on the iPad is shown in Settings > General > Available, the message that you are getting is a generic message e.g. if you've synced lots of music, or films/TV programmes from your computer's iTunes to the iPad, then change your sync options to de-select and therefore delete them from the iPad.

Or you can update via your computer's iTunes (Summary tab in iTunes), that should require less free space as it can use the computer (though that will download the whole iOS version, not just the update).

But however you update, take a backup first, copy purchases over to your computer's iTunes library (File > Devices > Transfer Purchases), and preferably take your own copy of any important documents/photos

My advice on doing ANY iOS upgrades/updates.

Ideally, your iDevice should maintain a minimum free storage amount of 4- 6 GBs or greater on any iDevice (the more free space, the better) , plus, more than 50%-60% battery status to ensure proper operation, as well as, to ensure the possibility of a successful iOS upgrade/update installation.

In addition it is best to upgrade an iDevice connected up to a computer running iTunes with you iDevice sync'd and backed up through iTunes rather than Over The Air (OTA) using a wireless WiFi connection, if this is possible.

Doing a major or critical OS upgrade/update can be risky to do over Wifi or cellular due to the potential of data interruption or data drop outs causing issues with the download of the OS data and the subsequent install to the device.

If you have no other choice than to use Wifi, then make sure you have a strong and stable connection signal the will not induce the potential for data drop outs.

Also, it is better to do the upgrade/update through iTunes as you'll get the entire upgrade/update and not just a smaller sized WiFi download version/portion that is based on your model iDevice that may or may not download everything your particular iDevice needs.

I prefer the iTunes method as there is minimal risk and I have never had ANY issues with ANY OS updates using this method.

Also, as a disclaimer.

I make no guarantees, expressed or implied, that any of my procedures will return EVERY older iPad to a usable, running condition.

First, connect your iPad to USB and sync and backup your iPad to iTunes.

Then disconnect/eject your iPad from the computer.

From just the iPad, in the Settings App under the General setting erase and reset your iPad to completely erase your iPad 2 and then, again, from the iPad, set it up as a new iPad setup to factory "out of the box" operation.

Then reconnect your iPad 2 to the computer and make sure to cancel the syncing, by tapping the small X to the left in the top center iTunes display box.

iTunes should detect your iPad and ask if you want to update to the latest iOS version.

Select OK. If iTunes begins to try and sync, again, cancel the sync. Let the update continue until it loads into the iPad.

May take anywhere from 30 minutes to an hour to update the iPad.

DO NOT WALK AWAY FROM THE COMPUTER DURING THE UPGRADING PROCESS!!!!

Once your iPad is updated and your iPad appears in iTunes, again, CANCEL the sync, once more.

Select Restore from Backup instead and pick your last backup to restore back to your iPad 2.

Once the restore is complete, finish setting up the iPad and let it sync back to iTunes you can either cancel the sync, again or let it backup, again.

Then disconnect the iPad.

Do one hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

Once your iPad is back to the Home screen,

In the Settings App under the General tab, to the right under Spotlight sesrch, try disabling the search under apps that really do not need a search, like some games, remotes, apps that really do not need to be searched, etc., to reduce the list for Spotlight to search.

Try turning on Reduced Motion.

This is found in the Settings App in the General tab the left panel.

In the right panel look under Accessibility, the look for Reduce Motion and turn this feature "On".

You should see an appreciable performance increase on all iPad 2, 3 and 4 models.

In the Settings App under the General Tab, in the right column, look for Background App Refresh and turn this setting to "off".

I update ALL my iDevices connected up to my iMac and sync'd over USB through iTunes.

I have NEVER, EVER had an issue with any iOS updates.

Good Luck!