It was a bit of a surprised to me as I had not saved my blobs, but cydia did for me. First you need to ever have been on 4.3.3 jailbroken. I dont think I can post links but if you google how to downgrade from 5.1 to 4.3.3, pick the web from redmond pie. You need TU to get your blobs from cydia for 4.3.3. Also at some stage youu will be asked to amend one file on your pc to trick itunes into thinking that the installation of the ios is checked against apple. Give it a got, the instructions are very clear on the website and ask if you have any question. Ah...also you will need to download the custom firmware for your version before doing all that.