Yes you can!
But:
- Make sure your windows system is 64 bit (as it is pretty recent, I gather it will be), otherwise upgrading will give you 0.
- Make sure the RAM you buy is compatible
- I suggest (especially as your graphics card is integrated in the CPU and uses that memory) you buy your memory so that it can work in dual channel mode (ie same size, so either 2*2GB, not much of an upgrade, or 2*4GB...)
- You sure you need that upgrade? did you check your ram was too low?