Even if you delete files, the storage capacity will not be restored.

Hi, 

Welcome to Box community!

Please keep in mind the following information about storage calculations: 

• Trash is excluded from your overall storage calculation.
• If you are collaborating with another user in a folder they own, the storage is calculated only as part of the owner's account and will not count toward your storage calculation.

The accumulated storage and/or number of files will be updated and may take up to 24 hours to be correct. If the issue remains unresolved after 24 hours, please inform me and we will investigate further.

For reference, you can visit this article: https://support.box.com/hc/en-us/articles/360043695334-Storage-Usage-Or-File-Count-In-My-Account-Is-Incorrect
 
Thanks for posting!

Best,
Ann