Try just pulling up on the top...on a lot of them it's held on with clips & just snaps off/on. Is your stitch length correct at the longest setting? Your dial should go from about 6 spi all the way down to stitching in the same spot. On all of mine (158.17550, Ultra-stitch 8 & Ultra stitch 12) there's an eccentric behind the stitch length dial. By loosening a set screw there & turning the eccentric you can adjust your stitch length.