Write a letter sending resignation.
Kindly accept this as formal notice of my resignation from the position of (job title, departmentetc), with effect from (normally date of the letter or receipt of letter). However, in accordance with my contract of employment I am happy to continue to work until (date that your employment ceases according to notice period, calculated from your stated effective date of resignation).
I would like to inform you that while I believe that I am moving for good reasons, I am sorry to leave, and I thank you for your support during my time with the company, which I have found enjoyable and fulfilling. It will be kind of you if you let me know the arrangements for handing back equipment, company car, etc, and handing over work and responsibilities.