How to downgrade my jailbroken iPhone 4 iOS 6.1.3 to iOS 6.1.2?

How do I downgrade to iOS 6.1.2 on my jailbroken iPhone 4 (preferably without losing any data). Please give detailed instructions.

Unfortunately, you'd have to reset your jailbroken phone while downgrading. To downgrade, get the firmware you want and then use that update while you're resetting.

Unfortunately, no you can't, even if you saved your SHSH blobs. Apple does not write the firmware anymore, which make downgrading back to 6.1.2 impossible.