All my picture folders (390gb) are stored on the hard disc so it is also almost full. MY first external disc drive is getting full (Time Machine). So I've purchased and mounted a second external drive. My objective is to move my picture files onto the new external drive so that LR will know that they are now stored on the new external. At that point I would delete them from the hard disc and rely on the backup disc and the second external for storage and backup. This is the solution the Apple folk recommended. They, of course, did not say how to do the transfers.
I am not an advance computer player so any help would be greatly appreciated,