Simple answer - No, Apple doesn't offer a means to upgrade the RAM (soldered in).
Complex answer - Still No!
Lets say you could desolder the RAM chips you are likely damage one or more solder pads and then there is the issue of what to put in place of the chips you took out. You would likely need to change out the driver logic to support the larger RAM and you might even need to run patch lines across the bd to get it to support the RAM you put in. Then you have the size issue are you able to find low profile chips of the larger size available that fit in the limited space? Then you have the heat and power issues to deal with.
By the time you did all of this the cost would be quite high and the reliability of the system highly questionable. I'm sure Apple at some future point will offer a system with more RAM than they offer today but I think thats at least a year or two away.