iOS update on iphone6

Dear All,

The version of iOS currently installed on my iphone6 is 9.2.1. Today WhatsApp stopped working and cannot be updated because of iOs that is not up to date.

Is it actually possible to update iOs 9.2.1?

According to information on my iphone, the updation of iOs is only possible using ITunes.

ITunes requies to attach my ihone to the Microsoft account. But to do that I should install Microsoft Edge on my iphone, that is not possible because iOs is not up to date.

Please help me to update iOs!