Aspirin only helps by somewhat thinning blood and reducing clots, but doesn't lower hct. Similar to those prone to heart attacks/strokes whose doctors tell them take aspirin.
Two ways to lower: give blood or find source of high hct and stop for 4-6 weeks. If really high (over 50) I'd deal with it right away. A good way to take it down lower than standard donation is donate double red cells (I think u can do this anywhere that does blood donations - red cross does it). I've done it and was a bit light headed for a couple days but was fine.
Someone in my family runs high hemo/hct so have learned how to manage and keep in a safe range.