Calculus is a required class for all cadets, there are no alternatives. The minimum for all cadets is Calculus II. BR2011 is correct, there is a summer school program over the summer where you can retake classes. I would say that you cannot get kicked for failing on course over the first semester, but failing multiples classes can lead to disenrollment.
All fourth class cadets take calculus I first semester, unless they validate. There is a second calculus one course during second semester where all of those cadets who have failed retake the course. Then, depending on the their major, they will take Calculus I in summer school. If the cadet is a government or management major, they will take calculus two first semester of their third class year.
I would recommend getting help as quickly as possible. There are plenty of tutors and staff willing to work with you.