Why can't i update minecraft?

I'm trying to connect to my friends minecraft world. It won't let us join, and i'm pretty sure its because we have different versions. Everyone else has version 16.1.0 and i have version 15.1.0. Its showing that there's no update i need to install. How do i update it?

You could always uninstall it then download and install it again, it should either have the up to date version available for download or a clean install should fix the update issue.