DVD File deleting

Know those wrinklies who are technology challenged - well I’m one!
I have what appears to be a simple problem - I cannot delete/move any files on a DVD. (Other CD/DVD seem ok)
I have an Acer with Vista HP, when using Win Explorer - Properties report disc full - but I know that it isn’t.
I want to delete some photos and also some outdated genealogical backup files (Yes I’m one of those anoraks!) I can send by email to myself but just can’t erase.
Apologies if this has appeared previously.
Any help appreciated.

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