On the left, in the Inspector, double-click "Record info"...
To change the whole song, even what was already recorded, create a new directory (such as "Move ya"), open the Pool and select "Pepare Master" , then chose the "Move ya" directory. Cubase will make a copy of all files your song uses, without copying unused files. Then delet the old files in order to free some space on your HD, and now work with your "Move ya" directory.