I would like to manage the avatars by being able to select the pictures to add to every specific avatar. Is that possible?
I'm sorry, but wpDiscuz doesn't have such a feature. All the settings you can find and manage in the Dashboard > wpDiscuz > Settings > Comment Thread Features admin page. More info here: https://wpdiscuz.com/docs/wpdiscuz-7/plugin-settings/comment-thread-features/#display-avatars
wpDiscuz supports all profile plugins custom avatars. Most of avatar managing plugins don't have front-end avatar uploading options, the best alternative for this is profile plugins (BuddyPress, Ultimate Members...) or forum plugin like wpForo which allows having full control to profile components.
I've been giving a try to both plugins (BuddyPress and Ultimate...) and none of them seems to affect the configuration of the comment itself, I mean, there's no field for customizing the picture of the user when trying to edit the comment, neither with the default editor nor with avada editor. May be once more I'm not doing it right.