Charges for iCloud storage

You can use another Apple device or a Windows PC as described in Downgrade your iCloud storage - Apple Support

See instructions in the section that starts with:

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.

Cancel by downgrading to the free 5GB plan. See: Downgrade your iCloud storage - Apple Support