Both. Running in series, you add the impedance, running in parallel you divide impedance by number of resistors.
So you'd run 2x speakers in series, that'll give 6ohm total. Run the remaining 2x speakers in series, that gives 6ohm. Run both strings in parallel for a total of 3ohms.
From amp + to #1/#3 +
From amp - to #2/#4 -
From #1 - to #2 +, from #3 - to #4 +