The image are dated from 2011 or 2012
Will they update to the latest Wheezy once plugged in the plug?
I would expect them to if you run an update.
I switched to wheezy just be editing my /etc/apt/sources.list
file to change all instances of "squeeze" to "wheezy" then doing an update. Well, I seem to recall had to remove an sgml package causing some odd dependency failure, and had to forcibly update one perl package manually, but apart from that it all went OK with several hundred (or >1000 - I forget) package updates.