how do i update an old ipad mini from 9.4.3 tp ios 12

If your iPad Mini is a First Generation iPad Mini, it cannot be updated beyond iOS 9.3.5

Identify your iPad model - Apple Support

If its a Second, Third or Fourth Generation iPad Mini follow the steps here:

Update your iPhone, iPad, or iPod touch - Apple Support

There isn’t an iOS 9.4.3.

If you’re using an iPad 2, iPad 3, or first generation iPad mini on 9.3.5, you can’t.

If you’re using an iPad 4 on 10.3.3, you can’t.

Otherwise, use the Software Update function or update it from iTunes on a computer.

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You can't. Your iPad 2 is not capable of running anything newer then that.

If you need to run iOS 12 you must replace your obsolete iPad with a new one.

Here's a list of every Apple device that supports iOS 12:

• iPad Air 1, iPad Air 2, iPad Pro (12.9, 2015), iPad Pro (9.7), iPad 2017, iPad Pro (10.5), iPad Pro (12.9, 2017), iPad 2018
• iPad mini 2, iPad mini 3, iPad mini 4
• iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPhone XR, iPhone XS, iPhone XS Max (iOS 12 is preinstalled on last three)
• iPod touch (sixth generation)