Student or Learner
First year is freshman
Second year is sophomore
Third year is junior
And fourth is senior
What do you call the 5th, 6th any special name?
Both high school and college/university are supposed to take four years. For people who take longer to complete college (maybe they took an internship, changed majors, etc.) we call them fifth-year seniors.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.