When you add a team member to your team you can choose if you wish to give them full access to your account or just access to one or more folders.
If you decide you want to change their folder access you can do this by doing the following:
1. Log into your account.
2. Click on the settings dropdown menu with your name on it in the top right hand corner and click on Account settings, then click on the Team members tab.
3. Once on the team members page, from the list of team members click the dropdown to the right of the team member. Then from the screen that opens up select the relevant option. Hit the 'Update' button and you're all done.