its based on how much reactions you receive some reactions give more reaction score points than others you change title when you receive enough reactions i think active member is the lowest and dex chan lover is the highest
edit: here is the link to the thread https://forums.mangadex.org/threads/list-of-forum-titles-by-reaction-score.1102077/
edit: here is the link to the thread https://forums.mangadex.org/threads/list-of-forum-titles-by-reaction-score.1102077/