iCloud storage

What happens when you decrease your storage plan

When you downgrade your iCloud storage plan, the storage decrease takes effect after your current monthly or annual subscription ends.*

If you downgrade or cancel your plan and your stored iCloud content exceeds your available storage, new photos and videos don’t upload to iCloud Photos, files don't upload in iCloud Drive, Messages in iCloud don't update, and your iOS devices don't back up. Learn how to manage your storage by deleting the information that you don't need anymore.

If you downgrade to the free iCloud Storage plan, you'll have 5GB of storage.

Downgrade your iCloud storage from any device

You can decrease your iCloud storage plan from your iPhone, iPad, iPod touch, Mac, or PC. Just follow these quick steps.

On your iPhone, iPad, or iPod touch

1. Go to Settings > [your name] > iCloud > Manage Storage or iCloud Storage. If you're using iOS 10.2 or earlier, go to Settings > iCloud > Storage.
2. Tap Change Storage Plan.
3. Tap Downgrade Options and enter your Apple ID password.
4. Choose a different plan.
5. Tap Done.

Downgrade your iCloud storage - Apple Support

https://support.apple.com/en-us/HT207594

Suggestion: Download the content you have been storing in iCloud to your computer, then downgrade to the free 5gigs.