I can't update my 4s from 5.0.1 to 5.1.1 by itune or the phone, message show "iso 5.0.1 up to date "

Good day

I am trying to update my iPhone 4s from 5.0.1 to 5.1.1 and a message show that ios 5.0.1 up to date !!!!

On other hand I try by iTunes & iPhone but it’s the same message

Also I reset the all setting and the same message show!!

However it went well by my x iPhone 3gs & 4

Regards

Abdulaziz Ali

titcat@hotmail.com