Take I-4 all the way in. You'll intersect I-95, but you don't really "get on" 95, as you're getting off the highway right at that juncture. Forget the exit labels, but follow signs for Daytona International Speedway as you're getting off I-4. It'll put you onto International Speedway Blvd. You'll pass the racetrack on your right. Just keep going straight, do not turn. You'll go up and over a bridge and wind up literally driving right onto the beach if you keep going (you can pay to park on the beach, it's cool).
EDIT: Just Google searched for clarification. I-4 to 95N. Just one mile on 95 and get off at exit 261. That puts you on International Speedway Blvd. Go straight until you see water...