Following the traditional product lifecycle and after nearly four years, Microsoft is about to end support of Windows 7 RTM (Release To Manufacture), the version of the operating system with no service pack on April 9, 2013. This essentially means that now is the right time to install Service Pack 1.
Windows 7 with SP1 will continue to have support until January 2015 following its Mainstream Support and until January 2020 for the paid Extended Support.
If you are unfamiliar what is included on the Mainstream and Extended Support the chart below will detail the difference between the two:
The Service Pack 1 (SP1) update will continue to have support for 24 months after the release of a successor service pack or at the end of the product lifecycle “whichever comes first.”
Download Windows 7 and Windows Server 2008 RT Service Pack 1 (KB976932) from the Microsoft Download Center here.
If you need assistance installing Service Pack 1 in Windows 7, Microsoft has a well-detailed guide on how to do this.
Source Windows Blog