Generally speaking, regardless of how good your grades are, you should not use the terms "with honors", "cum laude", "magna cum laude" or "summa cum laude", unless these honors have been conferred on you by the institution from which you graduated. Where such honors have been conferred, they will almost always be inscribed on your diploma, and they will also be recorded on your academic record.
If you graduated with higher grades than any other student, but were not awarded any of these honors, or if you attended an institution that does not award such honors, you can certainly say that you graduated first in your class; you would be foolish not to. I would not personally use the phrase "top of my class" unless I was referring to my performance in my final year at a secondary school.
Finally, the honors system summarised above, usually called Latin Honors, is most commonly used in the USA. It is also used in some overseas countries. The UK, and most Commonwealth countries, have different ways of awarding honors.