How do I delete all data and reset setting on iPhone 3GS when it not recognise passcode

I am trying to delete all data and reset an iPhone 3GS which no longer needed but it will NOT recognise the Passcode. I have tried all both with and without SIM card.

I can sign into phone and the sim card but will not allow deletion or reset. Any ideas please? Is it possible to do it another way?

Thanks

Rick