iTunes for iPad Pro

Buy more iCloud storage - Apple Support

1. Go to Settings > [your name] > iCloud > Manage Storage or iCloud Storage.
2. Tap Buy More Storage or Change Storage Plan.
3. Choose a plan.
4. Tap Buy and follow the onscreen instructions.

There is no app named "iTunes" on an iPad. There is an "iTunes Store" app and a "Music" app and other apps that have some of the functionality that the iTunes app on a computer had. If that doesn't help, you may want to reply with more information about what you are trying to do.

For buying music or using an Apple Music subscription see: Add and download music from Apple Music - Apple Support

Depends on what exactly you mean by "iTunes". And what exactly you are looking to accomplish.

The iPad Pro and all iPads have multiple apps that cover most functions of the iTunes application on Mac or PC.

It has the iTunes Store App where you can buy music, movies, Tv shows etc... Music App to play back music, the podcasts App for Podcasts, the TV app for Movies and TV Shows and the Books App for Books.

iTunes the Application is not available nor necessary on iPad.

PaulDW64 wrote:

Managing subscription like iCloud on an iPad Pro

The iCloud settings and subscription management is available in the Settings app.

Tap on the Apple ID / iCloud / iTunes entry at the top of Settings for subscription details, and the rest.