Well -

http://support.apple.com/kb/ht5540 (Instructions on how to upgrade/replace RAM on the 27-inch, Late 2012 and later)

iMac (Late 2013): Memory specifications (http://support.apple.com/kb/HT5908) (Article describing how the (21.5-inch, Late 2013) computers are not user-accessible)

We are an APPLE reseller. Give us a shot.

http://www.omegabroadcast.com/SearchResults.asp?Search=apple&Submit=Search