Did you complete an expansion of 500 bleachers and 100 lower tier since your last home game?
I'd advise to start with raising all prices by 10% (but set bleachers at 11). Then continue expanding your arena (spend about equal money on all seats). If you still sell out after the price increase (on 16-04), raise prices another 10% for the seats that sell out, and expand only the seats that sell out.