This is the directions I found to make files online only.
"How to make files online-only by default
To make all files that you add to the Dropbox folder on your computer online-only by default:
- Click the Dropbox icon in your notification center (Windows) or menu bar (Mac).
- Click your avatar (profile picture or initials) in the top-right corner.
- Click Preferences.
- Click the Sync tab. -
- Click the dropdown next to New files default.
- Select Online-only.
This setting means that all future files and folders that you add to the Dropbox folder on your computer will be online-only. New files won’t take up storage space on your computer. This won’t affect existing files and folders."
I do not have a Sync tab under preferences - now what