I'm not sure I understand your question, but here goes...
You may not need a plugin. Different users have different capabilities, depending on the user role they are assigned. Depending on how you have your Wordpress configured, new users who sign up are usually given "Subscriber" status by default.
Users who are "subscribers" cannot do much of anything beyond read posts.
Anyone who has a user role less than "Administrator" will not be able to make changes to the configuration of the site. Only administrators can change the site's display theme, or change the site's configuration options.
Here is the Wordpress documentation on user roles: https://codex.wordpress.org/Roles_and_Capabilities
If I have misunderstood your question, please clarify and we'll do our best to help!