1. Open the email editor in Advanced mode
2. Open up the image properties
3. Click on 'Use or Upload a file on MyGuestlist'
4. Right click on an image and select 'Resize'
5. Enter the width and height. If you want the ratio to stay intact when entering only a width or height, make sure the lock is closed on the right hand side.
6. Double click on the newly created image.
(It will have the width and height in the file name)
7. Wait for the image to display in your image properties, then click OK.