If you’re using one those plugins you might stumble uppon a notice in Dashboard about need of providing purchase key.

The Visual Composer (the same applies to Revolution Slider) is included in theme on extended/developers license, which means I bought it for higher price to be able to include it in my theme. You as end user can use it only with this theme, and do not get the license key that is used to auto-updates.
Updates of Visual Composer come with the updates of the theme ( I always include new VC in theme few days after release). You can of course buy your own copy of VC if you want it faster or need support from plugin authors, but that’s not┬ánecessary.