How do I merge two dropbox accounts together so there is only one?

At the moment you can only run one installation of Dropbox on a single computer and it can only be linked to a single account. Accessing another account from a computer where Dropbox is already installed (or any computer, for that matter) is as easy as logging in as another user through the Dropbox website. Otherwise, you can link accounts together by creating shared folders. Shared folders are designed to allow you to sync files between multiple accounts.

Please refer to the following link on more information regarding sharing folders: