Check your Windows Update if you have not set your Windows 7 to automatically install Updates. You will find Windows 7 Service Pack 1 (SP1) available for download.
First go to Start > “Windows Update”
Find the program called “Windows Update”
From there click “Important Updates are available”
Now you will see Windows 7 Service Pack 1 listed under “Important” category. Check and click “OK” to install it.
It is recommended to install this update. Depending whether you are using 32 bit or 64 bit Windows 7, the Service Pack size will be different as well. So what goodies does Service Pack 1 brings to us ? According to Microsoft on notes regarding to this SP1
Windows 7 Service Pack 1 (SP1) is an important update that includes previously released security, performance, and stability updates for Windows 7. SP1 also includes new improvements to features and services in Windows 7, such as improved reliability when connecting to HDMI audio devices, printing using the XPS Viewer, and restoring previous folders in Windows Explorer after restarting.
Aside from the feature and improvements Microsoft has mentioned, SP1 basically is a combo update for all previous released security patches as well. This update marked an important milestone for Windows 7’s product life cycle. As we just heard some rumors yesterday on the development of “Windows 8”, it is not doubt that time is clicking. At meantime go ahead and enjoying update your Windows 7.
Update: Here is the direct offline installer link
32 bit Windows 7 SP1 (537.809 MB)
64 bit Windows 7 SP1 (903.196 MB)
32 & 64 bit combo Windows 7 SP1 Update (1.9 GB) ISO image, need to burn or mount on a DVD