You can press the "Shift" key (the Get/Actions/Talk key) to grab a candle as it's flying through the air around the spectre.
As you're avoiding the spells the spectre is throwing at you, grab (shift key) a flying candle and then run it to one of the four candleholders in the corners. Click the shift key again to place the candle when you're close to a candleholder. Once you've placed four candles, you can attack and kill the spectre.
EDIT: Simul-post with friedeggs.
