How to get the seventh pokemon we catch in pokemon firered?? Plz help guys?

errrm what ?don't know what you mean ,could you add some detail .if you mean your party is full and you want to add one that you caught then go to a pokemon centre and click A when facing the pc(computer to th right of the desk)then click on the top option and then you wanna either
a)deposit the pokemon you don't want in your team then go back and click on withdraw ,and get the one you want
b)click move pokemon and then swap the one you want with the one you don't
I would maybe be more help if you gave details sorry :/