Presume you mean you're having issues permanently adjusting the order or assets (rather than just sorting).
If you can't reorder permanently, you may want to confirm that the folder is created as an orderable folder (see folder properties). If you're having issues on the very top-level folder of /content/dam, I think there is no way to make this an orderable folder without adjusting in the JCR (i.e. at http://localhost:4502/crx/de). If you don't want to permanently adjust the folder properties, you can also drag the nodes in the JCR into a different order and it should reflect for all users.