1) i'm a whole new person
2) i've completely changed (stress on com_PLETE_ly)
3) i'm a totally different person
4) i'm not whom i used to be (anymore)
When you say this to someone, you want it to be easily undrestandable, so
I AM NOT THE ONE I USED TO BE.
I AM NOT THE SAME PERSON I USED TO BE.
I AM A DIFFERENT PERSON NOW.