How do I upgrade the browser

Safari is an integral element of iOS/iPadOS - and cannot be updated independently of the OS. If your iPad has been updated to the most recent version supported by your iPad (the model and installed version of iOS have not been declared), then Safari is as up-to-date as is possible.

However, some websites incorrectly identify your iOS/iPadOS Safari User Agent when used in one or other of its browsing modes - of which their are two - these being Desktop and Mobile.

It’s easy to switch between modes if a website isn’t functioning correctly. From the desired web-page, touch the aA icon at the left of the Address Bar; this will reveal a menu. From the menu select Website Settings, then select (or deselect) Request Desktop Website, then tap Done. Now refresh the webpage.

The chosen setting will be saved for the selected website - and can be simply reversed if needed.

If you're talking about Safari, since it is a "built-in" app that comes along with iOS/iPadOS, it is updated everytime you update your operating system.

Regards

Giulio

Perhaps those apps do not support Safari.

Download an alternative browser (Chrome or FireFox).

You are welcome