Hi Audrey,
From what you've said and based on the previous reply, I think you made the error of putting the data on to a CDr. This counts as a one-off copy in that once the data's written it cannot be altered.
My advice would be to copy the data back from the CDr to an empty folder on your desktop, alter it as necessary, then copy the new data to a CDrw, which you can erase and record to again as you see fit.
Any troubles, yell,
Mark