TurboTax is printing a 1040A, but I want it to print a 1040. How do I do that?

When you enter your information, TT selects the ta return form that is appropriate for the data you enter.  If TT selected 1040A then that is the appropriate form for a simple return on which you did not itemize any deductions.  Why do you think it should be a 1040?

I understand that it does that. I'd just rather have it be a 1040 for future purposes. Do you know how to change it?

You cannot change it at least not on TurboTax.  I guess if you use the wrong tax form when preparing by hand you could use a 1040.   I cannot think of a good reason why you would even want to.  A 1040A is a completely valid tax return form.