How To Downgrade From iOS 7 beta To iOS 6.x and IOS 5.x
Step 1) – Download firmware 6.x or 5.x to download IOS page
Step 2) - Now connect your iPhone, iPod Touch or iPad to your computer via the Lightning connector.
Step 3) - Launch iTunes and go into the device summery tab. Now Option click on Mac or Shift click on Windows the Restore button and then select the iOS 6.1.3 or iOS 6.1.4firmware.
Step 4) - You will now simply need to watch your iOS device be restored back to iOS 6.x. If you experience an error simply place your device into DFU mode and then repeat the process from step 3.
Unfortunately it isn’t possible to downgrade from iOS 7 to a Jailbreakable firmware like iOS 6.1.2 even with saved SHSH blobs. The only devices that can downgrade back to iOS 6.1.2 with saved SHSH blobs is A4 devices like the iPhone 4.