Yes. If there are available seats on an earlier same day flight and you have a SAS Plus ticket, you just show up at the gate, and they will change your boarding card and ticket to that flight.
IT doesn't work for later flights. Here you have to change your booking to the later flight, either in the online booking tool, at the SAS service counters at the airports or by calling SAS. Depending on your ticket, this might be free of charge too.