My iPad will not let me update my iOS. Need iOS 14 for my financial software.

The first generation iPad Air, iPad mini2 and mini3 can only be updated to iOS 12.5.5. With this version installed, you will have one of these three models.

Apple ended major update support for these models of iPad in September 2019 - although they since continue to receive “point” security updates - the most recent being released just a few days go. These devices cannot be updated to iPadOS 13 (or any later major versions of iPadOS) as the internal hardware does not meet the minimum technical requirements (CPU and RAM) for newer versions of iOS/iPadOS.

Some App developers have dropped support for iOS versions preceding iOS 13.x for technical reasons (often because APIs or software libraries upon which they rely have been updated in the new version of iPadOS, making their App incompatible with earlier versions). 

Whilst many App titles remain compatible with your iPad, if you want or need to access to Apps requiring the most recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model that supports iPadOS15.

Sorry, I appreciate that this may not be what you were hoping to learn.

I hope this information provides helpful clarity as to your available options - and the fundamental limitations of your existing iPad.

Your iPad has gotten to as recent a version of iOS as it will get to, and iOS 13 and later are not supported, that<iPad lacks the hardware expected for newer versions, and there are no hardware upgrades available. Your options for newer iPadOS versions are a newer (used, refurb) or new iPad.