Q: how do I install itunes on my windows 10 pc

To install iTunes, you need to open your web browser, and navigate to the iTunes website, http://www.apple.com/itunes/download. It should automatically identify your OS and provide you a link to download and install iTunes.

As far as the backup, you can take a look at this support document about backups. It will identify where the backup is located. I'm not sure there is a way to change the default setting for the backup, as I've never attempted to do that. One support document helps you determine iCloud or iTunes for backup, and then where it is located at.

About backups in iCloud and iTunes - Apple Support

Find and manage your iTunes backups - Apple Support

If you're connecting to a new computer and don't have your old computer or backup with your library on it see Recover your iTunes library from your iPod or iOS device.

See Relocate iOS device backups for steps to store your device backups on an alternate path.

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