How to Cancel Dropbox
Navigate to the Dropbox website and login.
Make sure you back up before proceeding. To delete your account, first you must cancel all your subscriptions.
Click Upgrade and ensure that the Current Account Type is Basic Free.
Click Account and then Account Settings.
Select Delete My Account.
Dropbox will ask you to re-enter your password and give a reason for deleting your account. Afterwards, click Delete My Account.