How can I install the update for my IPad?

Settings>General>Software update.

But it depends if your iPad model supports the current iOS version. Identify it using these instructions:--> Identify your iPad model - Apple Support. The see this compatibility list:

You can never manually install ANY iOS/iPadOS upgrades/updates.

If your iPad is telling you your iPad software is up to date, it may, very well, BE up to date.

That stated,

A little hard to help/advise you when you provide little to NO useful information about your iPad.

Here are my questions to you.

Can you, please, confirm what year and model iPad do you have/own?

The “A” model number can be found on the aluminium back of your iPad, in very small print, right under the larger bold print “iPad” on the back of the iPad.

What iOS/iPadOS version is this iPad, currently, running?

What is the rated, internal data storage space/capacity of your iPad model and how much of this free, internal data storage capacity is left inside of your iPad model?

All of that additional info can be found in the Settings app, General settings panel, About.

Please try to make an attempt to answer all questions asked.

Thank You.