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OTA refers to over-the-air, updating without iTunes by going to settings->general-> software update.

You can also update without erasing anything in iTunes by clicking update iphone.

It's always advised to make sure you have a recent backup just incase anything goes wrong.
 
If I update to iOS 8 will it delete everything on my iPad?

Thanks

No. Not as a matter of course. However if something goes wrong the device can go into recovery mode and the only way out would be a restore.

so back your stuff up before you do an iOS update as a matter of practice
 
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