Account Settings

I have the wrong email associated with my account. It is an old non-existent email. When I try to update my email to my current correct email ... I get a message saying that address is already taken .... how do I fix this.

I have a question! So I got dropbox on my computer, after it asked me to login. Now the dropbox shows on my mac, when I open finder on the left side there is a folder that says dropbox and when I click on it shows all my dropbox documents. How do I logout? I like the idea of the dropbox folder there but I and not sure how…