Guys... The RAM is soldered on to the logic board and there's no way to replace unless you want to take the risk of unsoldering and resoldering RAM back on the board. I can almost guarantee that you'll have to buy a new system afterwards because this will permanently damage 99.9% of people systems. If you're really desperate for more RAM on your system you can buy a new logic board. However Apple custom orders these, so you'll have a very hard time trying to get a hold of one.
I'm also in the same situation as you. I bought an early 2015 13" Macbook Pro with retina display and I'm wishing i would've opted for a more top of the line configuration. It really sucks that Apple would do this however they tend to keep peoples devices running smooth with updates and as long as you stick to multi threaded applications and applications from the app store, you shouldn't have any performance problems for a long time. Keep in mind that the system you bought is very capable and is top of the line.