[runjake]

It helps to read the vendor-provided help, "how to share" is handily listed on the front page of Dropbox's Help Center:

https://www.dropbox.com/help/19

Summary: If you need more space, you upgrade one account and share the folders with your other users.

[JoeAltmaier]

Don't be a twerp. Of course we know how to share. But our shared files amount to nearly 2Gb, using up Everybody's allocation. So if they for example had half a Gb, they are now required to "upgrade" too.