If we look again in the Layers panel, we see that because we first converted the Background layer into a Smart Object, the Motion Blur filter was added as a Smart Filter. If you don’t think you added enough of a blurring effect, or maybe you added too much, just double-click on the Motion Blur filter’s name below the Smart Object to re-open its dialog box and re-adjust the Distance slider. Your changes will be instantly updated in the image (click OK to close out of the dialog box again when you’re done):