PLEASE HELP: Test Change Question

I signed up for the January 23rd Biology E/M test, but I now might want to take the Literature Test instead of the E/M test instead. Do I have to pay the $20-something fee or can I just leave it as “signed up for BIology E/M for January 23rd test date” and go in on that day and just take the Literature test and not the bio one?

I heard that one can sign up for any test basically (except language and listening test) and can just take another test without having to change the admission ticket online prior. (i.e. signed up for Math II but on test day takes U.S. History but registered online as taking Math II, says Math II on admission ticket as well)

Thank you so much!

i believe you can change your test on the test date.