If I have network access to a system, it is reasonable to remotely 
upgrade to a newer release or snapshot? 

If so, is there a good description of how to do it?  I think I have 
the big picture from reading the install document and doing it from 
floppies several times, but a checklist or detailed recipe would 
probably be a big help. 

Is it really (almost?) as simple as untaring the selected tar files?  
(being careful to save the old /etc)

What happens to the shell and tar/pax that are executing when they 
get updated?  Does tar/pax create a temp file and then do a rename?  
If so, does the old/dangling file continue to exist (without a name) 
until the use-count goes to zero or something like that?

Or would I have to copy what I need over to someplace safe, or rename 
the directories, or ...