How to upgrade Ram on Macbook air?

I have a late 2010 macbook air with 2 gigabytes of Ram. Unfortunately, the system alone uses around 1.2 gigs of it. Whenever I open an application on my mac for over 5 minutes it starts to become laggy to the point of where i have to force shut it off. Hopefully you anyone has a soloution.

Computer stats:

OS X Yosemite
MacBook Air (13-inch, Late 20100

Processor 1.86 GHz Intel Core 2 Duo

Memory 2 GB 1067 MHz DDR3

Graphics NVIDIA GeForce 320M 256 MB