I need help deleting photos and videos from my iCloud storage

For an intro to one common bit of confusion that can arise here, see ➡️ What's the difference between device storage and iCloud storage? - Apple Support

Deleting photos from iCloud Photos deletes those photos everywhere. Across all devices using that Apple ID and iCloud Photos. Everywhere.

Deleting stuff from iCloud will not alter the amount of storage available on an iPhone with too little local storage.

iCloud Storage can be managed, and can be increased to 2 TB.

Manage your iCloud storage - Apple Support

iPhone local storage cannot be increased. Your options there are to delete local data, or to transfer local data elsewhere, or to replace the iPhone with one with more storage. iCloud provides a handy place to offload local data.

Before deleting, consider creating a backup of the iCloud data ➡️ Archive or make copies of the information you store in iCloud - Apple Support

If you have your devices connected to iCloud photos, simply delete the picture on your device. That will move it into recently deleted. Then you can empty your recently deleted items (Warning:: those will then be deleted forever with no possibility of getting anything back).

https://support.apple.com/en-us/HT204264