How can i update my iPad to iOS 13.0

If it's a first generation model, it isn't capable of running 13 or above.

If it's a second generation or newer one, use a computer or the Software Update function in the Settings to update to 14.4.

If you're specifically trying to update to 13.0, you can't. Apple doesn't allow intermediate iOS versions to be installed.

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A first generation iPad Air, iPad mini2 and mini3 can only be updated to iOS 12.5.1.

Apple ended major update support for these models of iPad in September 2019 - although they since continue to received “point” security updates. 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 iPadOS14.

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 limitations of your existing iPad Air.