Charlee, that disk on the 403 pulls straight out. I always set my lever clear to the left and the up and down one at the center.... Be sure you find a zig zag disk - it makes a nice satin stitch. Nope it isn't as simple as the others you have but for a zig zag it is fairly simple. The 503 manual will work just fine - the only real difference is that the 503 has a cooler body for what it is worth. My brain sometimes feels picked.... Now I know why... It's ok I wasn't doing anything with it anyway.