have a old iPhone don't have icloud password

Okay i have a old Iphone 4s 16GB AT&T it was my dads who passed away. I like to give it to my 14 year old son to used and replace his Iphone 3g.We went to restore the phone on itunes and when we try to set it up for him it say it is lock with icloud.

I cant find any thing on my dads PC that has anything to do with Apple at all (his PC is windows ME) showingthat he did not used it much.

What im getting too is can I replace Logic Board to get around this. and if yes can i put in a 32 gig.

Thanks for any help yu can give me.