Chipset
 

K9K8G08U0M = 1GB
K9WAG08U1M = 2GB
K9NBG08U5M = 4GB

Just want to know whether it is possible to buy a 4GB chip (K9NBG08U5M) and take out the existing one (1GB) on my nano clone to make it a 4GB one?

I'm pretty sure you won't be able to get off your old chip without damaging your "mainboard", since its an INDUSTRIAL fixation by melting metal.
And also, you surely won't put the new chip on correctly without getting the whole thing messed up. Did you ever take a look at the size of the pins? No human could do it.. =P Just the Superman! ;D

Guest, I have read of people doing this but not always with success. You would need to find someone skilled in soldering of this nature as it is very fine work.