Changing your commission rate in the simulator is not done on the user side, but it can be done on the Admin side.
By default, your current commission rate is $4.50 per trade for stocks, and $4.75 per trade on options. These can be adjusted to whatever you'd like. Feel free to send us an email to firstname.lastname@example.org and we'll be happy to help you out with a commission rate change.
Our simulator is only designed to execute a per-trade commission rate and does not support a per-share rate at this time.
One more thing to consider is that when you get a new account number applied to your simulator, you'll need to inform us that you have a custom commission rate, as the commission rate from the old account number doesn't automatically carry over to the new simulator account.