If you want to upgrade to windows 7 professional enter this producct key
VTDC3-WM7HP-XMPMX-K4YQ2-WYGJ8
If you want to upgrade to windows 7 ultimate enter this product key
22TKD-F8XX6-YG69F-9M66D-PMJBM
Windows 7 Home premium product key : 6RBBT-F8VPQ-QCPVQ-KHRB8-RMV82