WP server permission problems

I’ve been using Woocommerce (with the Divi theme) with no issues, until I updated to Woocommerce 2.3 (and above). Suddenly I cannot add a Featured Image (get trapped in a media upload page); I can no longer append a link to text within the text window (simply won’t work); and I can’t add Tags (again, just won’t work).
I’ve been told this is not an issue bewteen the theme and plugin but that I have server permission problems. Though I do know how to change the server permisssions, I don’t know how to find the root of my problems. Which files or directories should I inspect, what would I be looking to find, and how should I change it/them?
Thank you.