How to manually upgrade from 1.1 to 1.3

The link provided at page https://github.com/mattermost/platform/blob/master/doc/install/Upgrade-Guide.md
is not working. (https://github.com/mattermost/platform/blob/master/var/log/gitlab/mattermost/current gives 404 error) Note: I'm trying to manually upgrade mattermost that is installed with gitlab.