Kindly note that your Dropbox folder and its contents will remain intact (therefore taking up space on your computer's hard drive). If you'd like to remove the folder as well, you can drag your Dropbox folder to the Trash.
This will delete your local Dropbox folder. Any files in your local Dropbox folder that haven't synced won't be available on dropbox.com.
I hope this helps and please let me how this goes!