Our company has recently released a new (type of product/model) which will replace the existing (product/model) currently being advertised in your (magazine/trade journal).
We would like to make a notice of the change of (product/model) in the forthcomming (month) issue, and kindly request your assistance in this matter.
Please call me personally on (XX) XXXX-XXXX to make the necessary arrangements, and to asist you with the required artwork, etc. I have enclosed a colour brouchure and a new price of the product.
Thanking you for your prompt attention to this matter.