Hello,
I am not sure I understand. Are you asking how to upgrade your players to use the latest HTML5 version installed by the kaltura-html5lib package or how to fetch source for a version that does not exist in this package from https://github.com/kaltura/mwembed/?
For the first scenario, it is very easy, go to KMC->Studio and hit upgrade on all relevant players.
For the second one, you can manually download the source and place it under /opt/kaltura/web/html5 the same way other versions are and then rerun the config scripts, but I would not recommend it. If that is your case, what exactly is the reason you need a version that is not included in the latest kaltura-html5lib package?
Thanks,