These are instructions on how to backup your SHSH blobs using Firmware Umbrella for Windows.
Download the latest version of Firmware Umbrella from here to your Desktop.
Right Click umbrella-4.1.13.exe and Choose Run as administrator from the contextual popup menu.
If you get a Windows Security Alert, make sure both boxes are checked, and hit Allow Access.
Make sure your iPhone is plugged into the computer and select it from the list of connected devices on the left
Click the Save SHSH button.
Once completed you will notice a new entry in the Saved SHSHs for iPhone list confirming the successful save of your SHSH blobs.
If Umbrella is not able to detect your ECID then you can find it and enter it manually. Use these tutorials to help you determine your ECID.