basically ,it is in admin panel language setting .in language string look for join now ,et list of related subject will come select the one u need ,then click on edit don't click on delete.
after clicking on edit join now clear it then save.
but as i said to make sure that u have select the right button try to edit first;let say instead of join now right something else the visualise ur site to see if the edit u juste make work and u have the right button .then if it's the right button string ,clear see more it in edit as state above and save it. i hope i have been clear this time.read it slowly u will get there.
anyway it all in the language setting.