I did it before. Today I tried reinstall sellacious from joomla store but it don't work - joomla shows link broken. This is why I have used the full version zip file. Joomla doesn't show any updates to do after check for updates.
So, I couldn't update it from automatic and manual steps, and I prefer reinstall Sellacious from joomla store to keep it automatically updated. I'll wait for a full version with quickstar and samples.
While updating manually it is recommended that you click on stop button and install extended package similarly.
which means after the core package is installed click on stop button before buffer completes and install extended package.
I hope this will solve this issue.
I tried update following the steps at Documentation but neither automatic and manual install worked fine. When I update the first file (pkg_sellacious_v2.0.0-beta3.zip), it finish and try to load automatically the second file (pkg_sellacious_extended_v2.0.0-beta3.zip)(c.png). Because it is unsuccessfully, I try to do it manually and the follow message error is show by clicling link below sellacious message (Alternatively, you can download the package from here and install it manually.) [b.png]