How can I expand the storage on my iPad Air 8GB ?

There is no iPad Air with 8GB. The smallest one has 16GB.

If you mean you only have 8GB left, then you will have delete stuff off the iPad to make more room. There is no way to increase physical storage space on an iPad. What you bought is what you stay with.

Alternatively you can use a wireless external drive to store videos and photos and other files so you can move the off the iPad. Apps however must be installed on the iPad.

http://www.sandisk.com/products/wireless/flash-drive/

You can't increase the amount of internal storage on an iPad (iPad Air's have 16, 32, 64 or 128 gig capacities). There are some wifi-enabled external drives that allow you to stream music, films, tv programmes to a device, otherwise you will need to sync content to/from your iPad as when you need it (you might also be able to redownload music, films and/or tv programmes depending upon your country and if they remain in your country's store).

There are some wireless external hard drives that can be used with the iPad.

Best iPad External Hard Drive Storage Options

http://www.unlocktips.com/2012/11/best-ipad-mini-external-hard-drive-memory-stor age-options/

iPad Storage Solutions

http://www.ipadstoragesolutions.com/iPadWirelessStorage.php

SanDisk Connect Wireless Media Drive

http://www.sandisk.com/products/wireless/media-drive/

SanDisk Wireless Flash Drive

http://www.sandisk.com/products/wireless/flash-drive/

WD My Cloud

http://www.wdc.com/en/products/products.aspx?id=1140

Another option:

Expand your iPad's storage capacity with HyperDrive

http://www.macworld.com/article/1153935/hyperdrive.html

On the road with a camera, an iPad, and a Hyperdrive

http://www.macworld.com/article/1160231/ipadhyperdrive.html

 Cheers, Tom 😉

1. Transfer all purchases from iPad to iTunes (computer)

2. Copy all photos, videos, movies and music from iTunes to wireless flash drive

3. Delete photos, videos, movies and music from iPad to free up space

4. You can now acess photos, videos, movies and music from the wireless flash drive via direct connection or wi-fi

Wireless flash drive.

http://www.sandisk.com/products/wireless/flash-drive/