Just last night, I finally got my wife's iPhone 5S (which she got in August) from iOS7 to iOS8. And did the same with her original iPadMini (which was stuck on iOS6, wifi only) last month. Both devices have only 16GB capacity, and both needed to have photos/videos removed in order to free up enough space to upgrade.
Given that she has an almost unused Windows Vista desktop computer, it was somewhat of a pain and an ordeal to transfer (save) those pics and vids before deleting them on the devices, then backing up, and then upgrading.
As others have stated, the 16GB models should not exist in today's market. I was shocked and disappointed that Apple scrubbed the 32GB models and kept the 16GB in this last go-round. Fiscally makes sense for them, but in turn also flipped the bird at their customers.
My own iPhone 6 and iPadAir are 64GB (I wanted the phone to be 32gb, but
well you know what happened there). My wife is stuck with her iPhone 5S for another year and a half before her next upgrade, but at least I can get her a newer model iPadMini with larger memory and cellular capability later this year.