How to tell my 6th form I'm leaving?

For irrelevant reasons, I decided I want to transfer from my 6th form to a nearby college that I'll like much more. I've got a confirmed available place at the college
But my problem is how do I tell my 6th form I'm leaving? I was planning on emailing and then also talking to them in person but I don't know what to...write in the email? Or who I should even speak to