Windows 7 was offered as a free upgrade to Vista when it first came out almost five years ago - any such free upgrades have long since expired.  You'll need to purchase an upgrade license if you wish to run 7. 
Hi, I bought an old Optiplex 760 desktop PC. It includes a license (sticker) for Windows Vista Home Basic which I have already installed. I seem to remember a Windows 7 upgrade program, but the page win7.dell.com is no long accessible. What are my options for upgrading this to a later version of Windows? Cheers!
Upgrading from Windows Vista to Windows 7 or later?