ios 10 is not available in my ipad mini 2

According to this list, iPad Mini 2 is compatible:

https://www.apple.com/ios/ios-10/

(your profile shows that you have a Mini?).

If you unable to get the iOS 10 to upgrade on your iPad Mini 2, it maybe that you actually have a 1st generation iPad Mini?

The 1st gen. iPad Mini is not compatible with iOS 10.

I have this problem too. My Model number (on the back cover) is A1490. It's iPad Mini 2. But when i go to Setting > General > Software Update, it keeps loading and said "Checking for Update..."

Have you tried upgrading to iOS 10 by connecting to a computer running the latest version of iTunes?

Already. My iTunes 12.5.1.21 and when i connected my iPad to my computer, and already sync it, it said "Connect this iPad using a USB cable in order to update or restore its software".

Have you backed up your iPad prior to iTunes in the very recent past?

You may have to do this.

If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

If you don't have a backup prior to this, either a previous iCloud or iTunes backup, you will lose all of your data on your device when you perform this procedure.