Avada - RevSlider - HTTP ERROR 500 error. Can 3rd party update plugin?

May 2016 site devloper created site with Avada. May 2018 I installed ‘backup’ of site on a new server. Revslider plugin stopped login. Via ftp renamed plugin folder. Logging in I updated the site 1st time since it’s birth.

Is it possible:

  1. for me to update the Revslider plugin?
  2. without losing it’s content?
    3 Would adding an SSL cert fix the issue?[is it a security thing?]
    What do I need to do to achieve this?
    On another note
  3. Is it possible to temporally unpublish pages [usually I would do this via the Wordpress interface resetting the page or post to draft and saving. This doesn’t work with the Avada theme the pages are still visible. I have not found where to alter the menu items yet.
    Thank you
    Re website: http://www.holisticwexford.ie/