Microsoft released Service Pack 1 (SP1) for Windows 7 earlier this year and it includes several security and performance related enhancements for Windows 7 all rolled into a single installer.
The easiest and quickest way to install this service pack on your Windows 7 computer is using Windows Update. However, if you have two more more computers running Windows 7, you may download the standalone SP1 installer from microsoft.com and apply it to all your computers even in offline mode.
There’s a third option as well. You may order Windows 7 SP1 on a DVD and Microsoft will deliver it to you via snail mail.