To change the account your computer is linked to, first unlink the computer in your account settings or desktop application preferences.
Unlinking your computer from your Dropbox account means Dropbox will no longer sync changes to the files and folders in the Dropbox folder on that computer, effectively turning off the Dropbox service. The files themselves remain untouched in your Dropbox folder.
When you unlink a device from the Dropbox website, you'll also have the option to remote wipe the Dropbox folder from the device.
When you unlink your computer, Dropbox will prompt you to sign in again with an existing account or create a new one. If you sign in with the same account, the application will seamlessly resume syncing your existing Dropbox folder (assuming you haven't moved or renamed it).
If you link your computer to a different account, the application may detect that a Dropbox folder already exists and ask if you want to merge it with the contents of your new account. If you choose this option, the application will copy the files and folders from the old Dropbox folder to the new one. Any files and folders that already exist in the new account and are exactly the same (that is, same name, location, and contents) will not be duplicated.
The merge option can be really useful if you want to transfer all of your files to a new Dropbox or combine two Dropboxes that have completely different contents. However, if the two Dropboxes have a lot of similar—but not identical—content, merging could cause problems. For example, if you have a folder in both Dropboxes, but the files in each version differ even slightly, the entire folder will be duplicated. In this situation you should probably choose not to merge. You can also avoid the choice altogether by deleting, renaming, or moving the old Dropbox folder before you relink your computer.