I'm getting confused as to what you're trying to do.
In your original post you said that your old EHD was used for backups. Therefore the only data on it is a copy of data on your main disc.
When you copy all your main data onto your new EHD your old one becomes redundant, as does the data on it, so you can do what you want with the disc. You do not need to move any data from it as your data will exist in two plces, your main disc and the new EHD. As I said earlier, I would use it for an extra copy of VERY important data.