So I am 15 mins away from the 5th ave Apple Store and just yesterday I sold my 2.0Ghz uMB on craigslist for $800. It was a 11 month old macbook. I want to buy a uMBP 13", the standard one with 2.26GHz, 160GB, 2GB. But the thing is I want 4GB. Can I just go to the store and tell them I want 4GB in it instead of 2GB? or I have to order online for that?