[H] Win7 Media player needs to extend on HD screen

[Winterlight]

I just hooked up a new laptop HP Win7 PRO HDMI port to my 58 inch 
Plasma TV. I am using Media Center for the first time. Everything 
works except the TV screen size is small in the middle of the screen. 
I need to extend it, but where do I do this, in Media Center,... or 
in video setup? Detailed explanation please. thanks