This tutorial explains how to close a Dropbox account. But prior to this operation there are several important points worth your consideration.
What happens when you close your account
At the end of this procedure, you won't be able to connect to the Dropbox website and access the files stored online. Make sure that you have an offline copy of all your important files stored on your computer.
Computers and mobile devices (Dropbox app) connected to your Dropbox account will stop syncing.
If you are using a pro account, then you will need to terminate your paid subscription before closing your account. You can downgrade your account HERE.
How to Unsubscribe from Dropbox
Sign-in to Dropbox. Click the tiny arrow appearing next to your name > Settings:
Go to Account Settings and then click on the Delete my account link:
A window opens and you will be asked to enter your password again. Choose the reason for which you want to close your account and click on Delete my account: