Board Thread:Support Requests - Getting Technical/@comment-24690905-20141115060310/@comment-452-20141115135624

To change the sort direction, click the arrow again.

This isn't actually mentioned on Help:Sorting.

By default, it shows an up/down arrow
 * When you click it once, it changes to an up arrow
 * When you click it again, it changes to a down arrow
 * When you click a different column, the previous header changes to an up/down arrow
 * If you hold shift, the previous header doesn't change, because it sorts by both columns (I only just learned this today, thanks M͢ystr͢ile!)