Kindly Take backup of your website and databse before updating it.
It's preferred not to upgrade live site and upgrade it over staging first, test it and then move it to live.
There are two ways to update Sellacious on your site.
Select the file with the name like
pkg_sellacious_v2.0.0-beta3.zip (version can varied). This is the core package of sellncious.
Note: It's mandatory that you install the core package of sellacious first(not extended).
Once the core package of sellacious first, you'll get the msg to Downlaod and Install automatically. Click on stop button and manully install the extended package of sellacious
pkg_sellacious_extended_v2.0.0-beta3.zip (version can varied).
While updating manually it is reccomended that you click on stop button and install extended package similarly.
2. Update from Joomla:
Note: Before updating ensure that the update is compatible with your Joomla! installation.