swapping my laptop hard drive?

Hi,
I currently have a 250GB HDD in my vaio laptop.
I purchased a WD passport 500gb external to swap with my internal laptop drive.

So my question is that should i just attach the external through USB and copy all files or do i need to run some program to make the external identical to the internal??

please let me know.
i dont want to mess up my windows and start all over again.


thanks alot for the help guys.