how do I get latest itunes version on ipad mini?

You download latest version of iTunes on your PC, go from there. https://support.apple.com/en-us/HT201352

There is no iTunes for iOS/iDevices.

There is an iTunes music/video purchase store app and the Music app for Apple Music and your own iTunes music library from iTunes on a computer.

What iPad Mini model do you have are what, exactly, are you looking to do on that iPad Mini?