You can only be a member of one Clan at a time. If you are already in one, you will notice that the ‘Join’ button is disabled. You will have to leave your current Clan first before you can join another one. 
To leave a Clan, click the ‘Leave Clan’ button. Once you’ve done so, you’ll be free to join another Clan or create your own.
Don’t worry, you will be asked to confirm your decision before you go ahead and leave the current.
Note: Although new players can still join the Clan while the event is ongoing, no member can leave or be kicked out while you’re on a journey to Adventure Isle!
_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
FarmVille Game GUIDE