Can you upgrade your dell Xps?

Hi all I just purchased a Dell XPS m1330 With the following specs:
Core 2 Duo processor (2.2 ghz)
Windows Vista
13.3"inch Screen (1280x800) resolution
2GB Ram
128MB 8400Gs Graphics card.
Wireless, Bluetooth
Camera, microphone
Finger print reader
9 Cell battery
Pre-installed Microsoft Office Enterprise 2007
2 year warranty
For £450... Was this a good deal?
and secondly can you upgrade your laptop once you already purchased it, as i want 4 gb ram instead of 2... Thank you.