Update:
There is unexpected issue with the update of this module specific so you can't update from 1.0.5 to 1.0.6 version at this moment.
We suggest you to backup your site, then download the latest version of JA VM product module: https://www.joomlart.com/member/downloads/joomlart/joomla-templates/ja-megastore
and install directly to your site.
Next time, you will be able to update via JA Extensions manager.
Again, remember to backup your site first.
We're sorry for any inconvenience it may cause.