The data in a RAID-5 set is spread across all of the drives. The only way to extract it will be to copy it to a different (ie, fourth) drive of sufficient capacity. Once you've done that, you can reconfigure the three drives and copy data back to them.
Thank you for the reply, in this case I think what I will do is save everything in one folder and RAR the folder in 4.5gb chunks and burn on the data to a DVD I am not wasting bluray discs for this... I have probably 800GB of data to save, its going to be a pain in the ass, unless i can borrow a drive or something.