The touch routine for udating is:
Settings>More>Application Manager>About Device>Software update>Check for updates
I have not gone so far as to Check for updates, because I don't know it I'd be forced to do an update at that point, and if so, to what version would the phone be updated? Lollipop? Marshmallow? Nougat? Oreo? Or would the update process only offer the newest update compatible with this old phone?