When i want to reset my old i-phone it prompts me for a restriction passcode. I do not know what it is - how do i retrieve it?

I purchased an i-phone 5s and transferred all info from the i-phone 4s to it. I now want to give the 4 to someone else but need to reset it first. It however requires a restriction passcode which I do not have.

When i want to restore it on my computer within i-tunes it prompts me to turn off 'find my i-phone' but if i want to do that it says there is no internet connection, surely due to the fact that I am now using a new sim card on the 5s

What to do?