1. Go to your administrator login page for your website.
Example: www.YOUR SITE NAME.com/administrator/ this can be different if your site is not in the root directory
Example2: www.YOUR SITE NAME.com/shop/administrator/ (Janice)
2. Login in using your login and password
3. Go to "Tools"
4. Click on "Mass Mail"

5. Write your message
6. Click "send" that is in the top right corner 
7. Done