How to update iPad to iOS 13?

I surmise that you have an original first generation iPad Air, an iPad mini2 or mini3. These models of iPad can only be updated to iOS 12.4.9.

Apple ended major update support for these devices in September 2019. They 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 iPadOS13/14.

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

Which iPad?

What iPad year and model do you own and what iOS version is it currently running?