IPHONE 4 16GB BLACK .

Iphone 4 16gb black on vodafone works fine but i updated it to new ios 6.1 and now wifi not working been told its software but now i cannot install the old version bcoz it says its already updated good for some one who knows how to do i, selling phone only nothing els it is on vodafone no offers no private numbers and no time wasters plz 07961700093