Navigate to the asset you want to edit then click it to launch a modal window:

You can only edit the following:

1. Tags, you can delete or add tags
2. The credit, you can modify or delete it.
3. Notes, you can add or delete them.
4. You can preview the image by clicking the preview link
5. If you need to download the asset, click the Download button.  The asset will begin to download within a few seconds.
6. Click Save Changes if you make any edits