Storage is not a live calculation, but calculated nightly for billing purposes.
Administrators have access to monitor storage and account usage through the Administration control panel and will be billed for the Peak Storage, the highest day's worth of storage, within their monthly billing cycle.
This means deleting content at the end of the month, before your billing cycle, will not reduce potential storage overages hit in that billing period.
To see current storage and bandwidth usage:
Choose Administration from the upper right drop down
Select Account icon on top navigation bar
From here, you will be able to view your Plan Limits, Storage, Peak Storage, Users, Project Totals, and SafeStream minutes used. The users tallied here are not a record of all users, but just the active ones (disabled/locked users do not count towards your package limits).
An alternative way to view this is in the dropdown of username in the upper-right corner of the account. Project thumbnails provide a real-time update on storage, users, and project file totals.