Q: Unable to update to ios8 even with 19gb of iCloud storage available

Hi Kiddieface,

Thanks for visiting Apple Support Communities.

If you don't have enough free space on your iPad Air to update to iOS 8, you may want to update using iTunes on a computer:

Update your device using iTunes

If you can’t update wirelessly, or if you want to update with iTunes, follow these steps:

1. Install the latest version of iTunes on your computer.
2. Plug in your device to your computer.
3. In iTunes, select your device.
4. In the Summary pane, click Check for Update.
   
5. Click Download and Update.
   
   

If you don't have enough free space to update using iTunes, you'll need to delete content manually from your device.

From:

Update the iOS software on your iPhone, iPad, and iPod touch - Apple Support

The storage in your iCloud account stores backups and personal data, although this storage space does not impact the update process:

When you sign up for iCloud, you automatically get 5 GB of free storage. Your iCloud storage is used for iCloud Backup, app data and documents stored in iCloud, and iCloud Mail (your @icloud.com email account).

From:

iCloud: iCloud storage and backup overview

All the best,

Jeremy