How to cancel Dropbox
Cancelling your subscription
To downgrade your Pro account’s subscription:
Sign in to the Dropbox website with the Dropbox account you wish to unsubscribe.
Visit the downgrade page.
To cancel your Dropbox account and subscription:
Sign into your Dropbox account on the Dropbox homepage.
Go to Settings under your profile name at the top righthand corner.
Go to Account in Settings.
Scroll down to Delete my Dropbox near the bottom of the Settings page. Click Delete my Dropbox.
Enter your password, your reason for cancellation and click Delete my account to finalize your cancellation.