count with IF condition in SQL

how i will add IF condition ,if for a single student there are five subejct data has been inserted then i want to restrict it for six data....as i have done this in below query but i cannot ad IF with this,,,

SELECT Count(Student_ID) as 'StudentCount' 
FROM tbCourseSemOne
where Student_ID=1 
Having Count(Student_ID) < 6 and Count(Student_ID) > 0;