Update iPad to iOS latest version

If your iPad is stuck on iPadOS 12, most likely it is too old to be upgraded any further.

Go to settings>general>software update and if that states that your iPad is up to date, and you have not any beta profiles installed, your iPad is too old to upgrade further

We cannot know what the latest version is for your iPad if you don’t tell us what iPad you have and what iOS version you’re on now. It may be that your iPad is already as up to date as it can be.