XF 1.4 Is there a way for users to join usergroups on their own?

I have some nsfw and political forums that people have to choose to join on my vb site. We're getting ready to move but I haven't been able to find an option in xenforo to do the same thing. Does it exist, or is there a work around?

I tried to make a free user upgrade but it requires a price higher than $0.
Do you know of one that exists currently? I tried searching but it;s kind of a difficult topic to find info on as it can be described many different ways.