I currently have 9.1 on a 6S+. I tried going through the usual upgrade process in iTunes and I got
This device isn‘t eligible for the requested build‘
I went through the proposed solutions at https://support.apple.com/en-us/HT201442
but nothing worked.
I've never had this problem before. I just checked the status of my certs, and they look fine. OS 10.11.4 and the latest Xcode seemed to have installed fine.
I've used the same Macbook Pro for dev for about 1 1/2 years, so I don't see this being an issue of my gear.
Any suggestions appreciated, but I could use specific and detailed instructions i.e. which UI to make changes in, specific drop-down menus, et al.