Do I mention in my personal statement that I am resting one of my AS's? How do I go about it?
Your PS is there to explain to admissions staff that you a) know what course you're applying to b) have the interest and motivation to stick out the course you're applying to c) have any non academic skills or experience to succeed on the course you're applying to
It shouldn't contain any information that is available elsewhere on your application - your education section should show any resits.