Join page instead message " your current..."

Hi, when a non-member click on one thunball, they receveid the message " Your current membership...", how i can redirect they to the join page ?

Thanks...

It needs a modification in the code I suppose..there are no options of doing this from the admin panel.I do not know if you can simply add a javascript code inside the language thing, I did not try that, but you can try.I am not sure it will work.