yes you can upgrade only SSD but ram not able to upgradable.
No it is not upgradable everything you get on the initial purchase is what u get so if ur getting the 15 inch retina then u get 250gs of memory and 8gs of ram standard, u can upgrade to 16gs of ram or 768gs of flash memory but it all has to be done before you buy it, once u buy it u can't upgrade anything since everything is on the motherboard no moving parts. 250gs and 8gigs of ram is pretty good for the average user but if you are a heavy video and picture editor u could upgrade but u need to do it before u buy it u could also use a external hard drive and save files there and save urself a few bucks.
Sadly, no. Everything is soldered onto the logic and is not replaceable. Therefore, you cannot upgrade anything on the Retina MacBook. It's unclear if Apple is willing to replace/upgrade memory/storage post-purchase, although it is very unlikely as the entire logic board would need to be replaced.
answered on June 8, 2013