Well I see you are already upgrading, so that's a good thing. Invest rationally - don't break the bank for each upgrade, but rather spend only half of your money, for exampe. Unless you are sure you won't need any money in the near future for new players, coach, doctor...
Also your prices need a bit of correction - I saw you have already changed them. Bleachers to $12, Lower Tier to $45 and Courtside Seats to 145. You don't have any Luxury boxes yet, but you can change the price already to $1.500. In the next batch of upgrading, do not forget them - build 5-10 of them