Open Settings on your iPhone or iPad
Tap your name
Tap iCloud
Tap Manage Account Storage or Manage Storage
Review what is using space
Delete old device backups
Delete photos and videos you no longer need
Turn off iCloud Photos if you do not want to store photos in iCloud
Delete large files from iCloud Drive
Remove old messages and attachments
Delete app data you do not need
Empty the Recently Deleted album in Photos
Empty the Recently Deleted folder in Files if available
Delete email attachments from iCloud Mail if applicable
Remove unused apps from iCloud backup
Reduce the size of future backups
Upgrade your iCloud storage plan if needed