There’s no exact “setting” in the backend/Admin UI. You’ll have to edit your template files (the php files that are in your theme folder). Search for something like <a href=""></a> where you got one (or more) of the php (wp native) function or variable:
the_author_posts_link();$curauth->user_url;get_the_author();get_author_posts_url();- … or something theme specific
Helpful is always a link to the download of your theme or some template code.