Dropbox description from the Google Play Store.
Dropbox is a free service that lets you bring all your photos, docs, and videos anywhere. After you install Dropbox on your computer, any file you save to your Dropbox will automatically save to all your computers, your Android device, and even the Dropbox website! With the Dropbox app, you can take everything that matters to you on the go.
Read your docs or flip through your albums when you're out and about. Save photos or videos to your Dropbox and share them with friends in just a couple taps. Even if you accidentally leave your Android in a taxi, your stuff is always safe on Dropbox.
Features: • Always have your stuff with you, no matter where you are. • Save photos and videos to your Dropbox. • Share your photos and docs with family and friends. • Save email attachments straight to your Dropbox. • Easily edit docs in your Dropbox.
I will put more information here and the help section for DropBox should probably be the first place you look.
- To remove a user, click on Sharing.
- Click on the folder you wish to manage.
- Click on the down arrow and you will get the option to "Email" or "Kick Out for each member of that folder.
This service is so good and you will find much better help on their own site, so if you click the help link above you will find just about anything you can think of there.