to answer your questions:
Yes - you can file a support case at any time from under the Help tab of the site if you do not already have your account preferences set to use the "modern" gallery. That setting in your preferences shifts the gallery being appended to your listings to the HTML 5 version, which does not use Flash.
If already have this marked in your account preferences, your listings will be using the HTML 5 version of the scrolling gallery. If not, you can file a case letting us know you wish to change this on your Active Listings and we can run a command to remove the old version and replace it with the new version on Active Listings that are eligible for revision on eBay.
Yes, for listings that are eligible for revision on eBay, we can run a command for any account that has a valid eBay token to remove the gallery from those listings.
So, after logging in to your Auctiva account please select "Acct. Preferences" from the My Account menu and in the "Listings Enhancements" section of the preferences there is a checkbox for "Enable the Modern Scrolling Gallery" which you will want to check (and then save the changes) if you have not done so already. Listings posted after that will use the HTML 5 gallery.
If your listings are not already using this, you can then file a support case letting us know and we will be happy to run the command to change the gallery on the active listings.