How can I change read/write permissions for a DVD RW?

I've some files saved onto a DVD RW previously and would like to add on more files to it. However, it doesn't allow me to do that. When I checked the file info, it says that I have read & write privilege, but at the same time, there's another line that says "You can only read". When I clicked on the lock to attempt to make changes to settings, nothing is clickable. Take a look at the screenshot below and you'll know what I mean.

Can anyone advise on why this is happening?