upgrading t46 from 28.73.0.50 to 28.80.0.70?

[asinshesq]

I've got two t46s with 28.73.0.50. What's the right way to upgrade to the latest? The release notes for the new firmware say that you should go from 28.73.0.50 to 28.80.0.60 or from 28.73.0.60 to 28.80.0.70...how do I go all the way from28.73.0.50 to 28.80.0.70? I don't see an interim release taking me from 28.73.0.50 to 28.73.0 60 so I don't get what I am supposed to do.

Also, will my config get messed up when I upgrade? Do I need to back up before installing the new firmware and then restore when I finish installing the new firmware?

Thank