Why do I have a duplicate Dropbox folder?

I had to reset my Dropbox password recently and for some reason upon signing in again on my Mac it seems to have duplicated my Dropbox folder.  I wasn't aware of this at first but it seems I've been saving some files in what seems to be the unlinked folder and some in the linked one.   I have no idea how or why this happened and there was no period of copying or downloading that I noticed.  The old one seems to be in ~Library/CloudStorage along with the new one.  The new active on of course has the Dropbox logo beside it.  'Get Info' doesn't give me the folder size of the old one but the size of the CloudStorage folder is under double the new Dropbox folder.  This is slightly suspicious.  Obviously my concern is losing documents and now figuring out a way of picking out files that are only updated in the old offline folder.  This could take hours.  

 

Is there a neat way of merging both folders with priority set to keep all new updated files?

 

Thanks