Hi my iCloud is full how to I backup

Read this support article for instructions on how to upgrade to iCloud+ or to a higher level plan if you already have iCloud+ --> Upgrade to iCloud+ - Apple Support

This article tells you how to manage your iCloud storage --> Manage your iCloud storage - Apple Support - including seeing how much storage you have and how to delete items stored in iCloud such as backups, photos, files, mail, messages and voice memos.

You have three choices. You can mange your iCloud storage and exclude some items from the backup to free up space.

Manage your iCloud storage - Apple Support

You can use a computer to backup.

How to back up your iPhone, iPad, and iPod touch with your Mac - Apple Support

How to back up your iPhone, iPad, or iPod touch with iTunes on your PC - Apple Support

Or you can buy more iCloud storage.

Upgrade to iCloud+ - Apple Support