Out of iCloud storage space

If my phone has 8 GB of pictures, (that is all i back up,) currently, I have an iCloud storage plan of 50 GB, how am i out of storage space? Clearly backups are not appending, but new separate file or instances of backup are occurring during each backup, each taking 8 GB each. Mathematically, 50\8=6 I should have (6) 8 GB backups...How do I delete old backups to make room for new? Thanks