I have Messenger already on my computer but changed e-mail addresses do I have to reinstall messenger?

How do I get it to work from more than one e-mail? Must I download it again? I need the exact steps. I can re-download it if necessary but that seems like it would waste space on the harddrive (having 2 copies).I have Messenger already on my computer but changed e-mail addresses do I have to reinstall messenger?you shouldn't have to download the messenger again, just go into the messenger and update your email address.