What if I want to downgrade instead of upgrade? Do I lose my photos?

You can change plans in either direction from the Subscription page, and no data is lost when you switch — that's stated outright. The practical catch is capacity: if you drop from 1 TB to 100 GB while sitting at 300 GB of photos, you're over the limit of the smaller plan, and you'd need to trim things down or move stuff to cold storage to fit. The platform won't quietly delete your work, but you do have to get under your new allowance eventually. Best to sort the storage maths out before you downgrade.