Can i replace existing single core processor with new dual core processor

I would guess that your netbook has a its CPU soldered on to the board. This would stop you from upgrading at all.

I agree, you're most likely stuck with that CPU. You could always look into overclocking it a bit.

Welcome to the forums!

Unfortunately, Intel Atom processors are designed to be permanently soldered to their motherboard and are not user upgradable.
Likely, the only upgrades you could perform to your current netbook would be to add more RAM, a larger HDD or a SSD.

Unfortunately, even the desktop atom boards have the processor soldered on.  

You're better off with a dual core Pentium or similar, it uses just as little energy and is a lot more powerful.