Where can i see my back up photos? Can i delete some photos in icloud back up?

I can’t see previous photos

You cannot view the contents of an iCloud Backup or delete photos from it. You can only use the backup to setup a new device or to do a full restore on the device. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

iCloud Photos is another option for photos. If you have iCloud Photos turned on, the photos on the device are the same as on iCloud, with the possible exception that some of them may be space-saving optimized versions if you have that option turned on. You view them in the Photos app on an iOS device. You can also login to icloud.com and go to the Photos app there. See: Set up and use iCloud Photos - Apple Support

If you delete any iCloud photos from a device or from iCloud, they will be deleted on all devices where iCloud Photos is turned on and from iCloud.