Q: Can't restore in iTunes ?

Hi all,

I recently gave my daughter my old 5s. Consequently her 5c has gone to her younger sister. I've gone into settings and tried to erase all data. It's asking for the restrictions code which we can't remember setting up. So after trawling the net I've tried all the solutions inc going into Terminal on my imac etc and also doing a force restore in iTunes. I get the message that the device isn't eligible for the requested build. I've checked my router and firewall settings as advised to no avail. I've yet to try from another computer as advised. Is there any way to get this back to factory settings so my youngest can have a fresh phone ? I know for a fact I never set a restrictions code and my daughter says she never either so not sure how it's happened. I am contemplating entering the passcode wrong on 10 or more occasions so as to wipe it clean ? Will that then allow me access to it as a fresh phone when her Sim turns up ? I've also gone into find my iphone on my daughters 5s and selected her 5c and told it to erase phone. Even though it's connected to the internet it won't do it. I'm stuck fast any help would be appreciated.