I want to downgrade back to the free 5GB of iCloud storage. Help!
How do I downgrade back to the free 5GB of iCloud storage?
See the section "Downgrade your iCloud storage plan" in:
iCloud storage upgrades and downgrades - Apple Support
You can decrease your iCloud storage from your iPhone, iPad, iPod touch, Mac, or PC. The downgrade should take effect after your current monthly or annual subscription ends.