Can't update.
hi how do i update my iPad mini iOS 9.3.5 into iOS 10?
iPad mini Wi-Fi
You don't.
The 2012, 1st gen iPad Mini cannot upgrade/update beyond IOS 9.3.5/9.3.6 for cellular data models.
The internal hardware in older iPad models are too old, now, too underpowered to upgrade any farther.
And this is a moot point now, anyways. it really doesn't matter, now, whether or not your old iPad model can upgrade/update, or not, to IOS 10.
Here's why.
Tap and read my link below for my additional info about your iPad model.
If you own OLD 8 and 9 Year Old iPad mo… - Apple Community
So Sorry & Good Luck to You!