how can i change fedex ground service price to $0 right now showing $16.43

You can't as far as I know.
If you want to do free shipping with the option of expedited shipping such as next day via Fedex you have to use the table rate module and edit the fed ex module to not display the ground option.
It's kind of a pain especially if you are new to CRE.

Hi bhavani,
I've been able to change the pricing of various shipping methods by looping through the $quotes and methods array (inside the order_checkout.tpl.php) File, and changing the values on the fly. But then you also have to change a few session variables because the Order Total function is a little bit tricky... took me forever to figure it out! Let me know if you need a hand...