Yes you can as long as it hasn't been installed before and you have a valid key.Make 100% sure that you read the compatibility notes once you have done this as it may effect some of your hardware/software after you install windows 7.    Let me know how it goes or if you need more guidance.   Thanks, Lance 
HI,     CAN SOMEONE HELP ME ON THIS? CAN I INSTALL WINDOWS 7 DVD DISC UPGRADE ON MY LAPTOP THAT CAME ON MY BROTHER'S LAPTOP FREE WINDOWS 7 UPGRADE? THE DISC WAS NOT YET INTALLED ON HIS LAPTOP...
WINDOWS 7 UPGRADE