You'll be fine if your AS flight is on time. Your DL flight should depart from the S concourse. As soon as you get to SEA, follow the signs and make your way to S. It will require a short train ride. 2 if you are unlucky.
Seems you arrive at SEA at 630pm and depart at 730pm. You can try for the earlier AS flight which arrives at 455pm if you want a bigger cushion.