I got a new Air back in January (currently running 10.7.5), replacing an old Macbook that crashed. The old Macbook has been backed up via Time Machine to a 1.5 T external hard drive. I'd been keeping the old Time Machine around, in case there were things that I needed to restore, but now that the new machine has been running for several months, I don't really need the exhaustive files. Still, just to be safe, I would like to keep the final backup of the old machine. I now would like to use that hard disk to back up the new machine-- but there isn't enough space to do that, because the backup of the old machine is taking almost all of the space, nearly 1.5 T of storage. What I need to do is delete all the old backups except the most recent. As far as I can tell, the only way to do this in Time Machine is to delete them one at a time, and with each one, answering "yes, I really do want to delete this" and entering my password. There are hundreds of backups, and this would take forever to delete one at a time. Is there an easy way to do this?