Thanks for answering my question.
For anybody who hasn't used Manage Attachments, click on the Manage Attachments button below the post editor box and you will see near the top of the upload manager:
1. Click Add Files to upload new files or select from existing files below
Then inside the box at the bottom labeled Attachments:
2. Drag previously uploaded files into this area to attach them.
Newly uploaded files will appear in the Attachments box. You can also drag existing images from the Home box into the Attachments box. Click on Done and the files will be attached to your post. You can select the insertion point for each image.