Release /Completion Dates

My release date was incorrect, so I added a correct one and went to delete the previous one, and the system won't let me. It's on the page, but not in the add/delete update system.Also, I've included my completion date, but there's no date on my film so it doesn't appear on my credits list in the top position, but is instead at the bottom. How do I correct this.

Thank you.