If you want to remove your Box.com file sharing account, you can easily do that in the Settings of your account.
I’ll show you below how I managed to close my profile using a desktop computer:
1 Go to www.box.com
and log in by entering your email address and password on their site.
2 Select Account settings
It’s in the top right corner.
3 Scroll down to Account information
Where you will see > Cancellation: Deactivate your account (this account is permanent).
4 You’ll see a warning that if you cancel, your files will be
removed and no longer available
Just Continue with the cancellation.
5 Indicate what’s the main reason for cancelling
Submit the answer and cancel account.
A message appears: Your account has now been deactivated. You’ll be logged out automatically and your account has been closed.
*Source (& thanks to): Box.com