how to update software on ipad 1?

You clearly don’t have an original first generation iPad - as this is limited to iOS 5.1.1.

I surmise that you actually have an iPad2, iPad3 or first generation iPad mini. These devices can only be updated to iOS 9.3.5 (WiFi Only models) or iOS 9.3.6 (WiFi & Cellular models).

Apple ended update support for models in September 2016. They cannot be updated to iOS 10 or later major versions of iOS, as the internal hardware does not meet the minimum technical requirements for new versions of iOS/iPadOS. This limitation cannot be bypassed; these older models are all 32-bit architecture devices, whilst all recent versions of iOS/iPadOS are designed for 64-bit hardware platforms. The iPad2, iPad3 and iPad mini1 are obsolete.

You may wish to consider that compatible Apps for older models of iPad are increasingly difficult to find - as third-party developers are increasingly dropping support for older versions of iOS preceding iOS11/12/13. As older versions of Apps are removed from the Apple App Store, you’ll not be able to (re)download or install them - which may severely limit the usefulness and utility of your iPad if you should you ever need reset or restore your iPad. As such, if you want or need to access most current Apps, requiring more recent versions of iOS, you’ll need to consider replacement of your iPad with a newer or current model.

Of current models, even the entry-level iPad8 has specifications and capabilities that massively outperform you current iPad - and is compatible with the vast majority of current Apps. Other models are more powerful still.

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

This is never going to happen.

Your iPad model is too old, now.

The internal hardware in that iPad is too old, too underpowred and completely incompatible with all later versions of iOS/iPadOS.

Virtually, all third party iOS app developers ended/stopped/abandoned supporting these old iPads over two years, ago.

There are virtually, NO MORE older iOS 9 or 10 compatible apps available from the Apple iOS App Store, any longer.

There are NO MORE popular, useful apps or games for these old iPads, any longer!

Especially games as game makers push for upgrade compatibility for best interactive user and cross device gameplay.

AND, that over 4-year old default iOS Safari Web browser is too old, not secure and not safe to use to access the Internet, any longer.

There are virtually NO MORE third party Web browsers left for 8-10 year old iPads!

Available and more popular third party Web browser choices are pretty much GONE, now.

If you must use these old iPad models, here is what is left for still updated Web browsers.

Pickins’ are slim, now!

ALook Web browser

Dolphin Web browser

Maxthon Web browser

TOR private browser

TOR + VPN private browser

Turbo VPN private browser

Sorry.

There is one last thing you can try/attempt, if you need an older version of an app.

If you own much newer iOS device that can run either iOS 12 and.or iOS/iPadOS 13 and later, you can install the most recent app/s onto that more recent iOS device.

Then go back to your older iPad, open the iOS App Store, go to the Purchases section of the store app, search for the app/s you wish to try and download to that older iPad and see if an older version of the app is allowed to be downloaded/installed to that older iPad.

These newer iOS/iPadOS devices must use your same Apple ID user account and password.

Failing that OR IF NO joy, then there is nothing more to be done.

If you need/want an iPad with an up to date iPadOS with access to current, updated apps, then you really need to seriously consider a new iPad model OR a much “newer”, less expensive, used iPad model capable of running the latest iPadOS versions. There are plenty of newer, older iPad models that can run the latest, current versions of iPadOS.

Sorry & Best of Luck to You!

A first generation iPad mini can not be updated beyond iOS 9.3.5.