As this manual is for both Joomla and Wordpress. Please read usergroup as siterole and vice versa. Screenshots are taken at random per CMS.
This advanced function is unique and very powerful allowing front-end users to change themselves into (certain) other groups without the administrators' interference.
In the advanced config option area change "Allow group change" to 'yes' and a button will appear.
Click on "Show table settings", a panel pops-up.
Understanding the table feature:
In the above example a user belonging to the “Author” group may change himself into “Editor” or “Guest”. Once that user is “Editor” he is allowed to change himself to “Author”, “Guest” or “Manager”.
Do not forget to hit the 'save' button scrolling down in the panel!
Note: if you do not need this feature please set “Group changeable” to 'no' saving huge DB queries.
On profile edit view of a user account
Now the user can change himself to another usergroup according the table settings.
Upon usergroup change and save, the user will be logged out automatically. He needs to login again to see the changes.
Password protected groups
If option “Usergroup entry password” option is set to 'yes' a front-end user can only change himself to a usergroup when he has the appropriate password available for. Read here