DD-A300GX deleteing titles from open Dvd+rw help needed

If I have 3 or 4 recordings on a Dvd+rw (not finalized) and do not have enough time for another recording, I delete one of the titles but the DD-A300GX does not seem to use this deleted time and stops the timed recording because of lack of space.
If I chose to overwrite the deleted space then the available space is not used.How do I combine the available space and the deleted space ?

Thanks