How do I delete this app?

I've had dropbox on my laptop for a while but never actually use it, the app is 474mb so is taking up a lot of room and I want to delete it. But every time I try it says dropbox cannot be deleted because it is still open, when it isn't open? I've tried everything, even when I go to the force quit option, dropbox doesn't show up because it isn't actually open. I have no idea how I can delete it... help???