How can I access the photos in my iCloud and how can I delete them?

How can I access the photos in my iCloud and how can I delete them?

See -> Manage your iCloud storage

Manage your iCloud storage - Apple Support

I've been getting notifications on my phone saying I have no space

Do you mean iPhone device storage?

Then try to free up iPhone device storage see this Apple articles below:

If you need more space for an update on your iPhone, iPad, or iPod touch

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

How to check the storage on your iPhone, iPad and iPod touch

How to check the storage on your iPhone, iPad and iPod touch – Apple Support (UK)

Clear Other storage on your iPhone or iPad

Clear Other storage on your iPhone or iPad - Apple Support

If you do not have the ability to delete Photos on your iPhone, go to: https://icloud.com - sign in with your Apple ID and go to Photos. There you can see all the Photos stored in iCloud, you can also clean up and delete the photos you want.