Iphone 4 downgrading iso version to 5 rather than 6.1.3?

Is there any way i can download my iso version of the phone i'm on 6.1.3 and i'm sure you can work out why i want to downgrade but i can't find a way on the net that does work, many thanks

also it is on uk vodafone.

Many thanks in advnace

Added (1). If i have what saved

If you have your shsh blobs saved you can downgrade to 6.1.2 with the new redsn0w.