Disable automatic backup when updating the iPhone's iOS -> How can I?

How do I disable the auto-backup every time I want to update my iPhone using iTunes!?

It always happens right after iTunes finishes downloading the new iOS update file; it will automatically perform a backup.

This is so stupid and annoying—I don't want to create any backup of my iPhone on my computer, ever!

I attempted a number of what seemed to be non-solutions, but none of them were successful.

Furthermore, my machine doesn't have adequate storage to produce a backup this size, 500 GB.

Thanks.