Hello Chloe,
Thank you for posting your question in our community, it is possible someone set the file as read only permission. Please can you save as and rename the file and see if you can now delete and save as you want ?
You can also remove the read only permission by doing the following:
You can check the file properties by right-clicking on the file and choosing Properties. If the Read-only attribute is checked, you can uncheck it and click OK.
Please let us know if the issue persists after that.
Best Regards, Asher