At this time, it is not possible to prioritize your downloads by specifying which should download first.  However, there is a manual workaround you can do when several files are in the process of downloading.  To do this, you will need to pause the files that are downloading ahead of your preferred file.  To pause files, find the torrent in your Torrent Feed, then click the blue text that says ‘Downloading’.  This will pause the torrent.  Alternatively, click on a torrent in your Torrent Feed, then click Actions, then click Pause.