In order to determine this, you'll need to refer to your prior year return.
You are not able to switch freely between methods. If you want to use the standard mileage rate method in any year, you have to do that the first tax year you use your car for business. Then, you can freely switch back and forth. However, if you use the actual expense method in the first year, you need to always use the actual method for the vehicle in all future years.
For more information, see Standard Mileage Rate vs. Actual Auto Expenses
