Move selection to parent folder

If using expanded folders with a few files, drag and drop is usually easy and as fast as using a button. With larger structures, the parent folder may not be visible, but the breadcrumb can help in that case (you can drop to the breadcrumbs).

If you really want a button, you should go and check the thread linked below, there are several examples revolving around this, including one moving everything from the current folder up one step in the folder hierarchy (beware that this will use the currently displayed source folder, not necessarily the one you're looking at if you have expanded some folders ... but it can certainly be adapted).