I have an image style in Drupal 7. I attached several images to a nodes and display the images based on this style. I then changed the effects on this image style but the existing images are not being recreated with the new image style effects. They show with the old image style effects.
If I attach new images, they use the new effects. Deleting an existing image and re-uploading causes the image to use the old effects.
This is a bug with image styles. If you are editing an image style and edit an effect that is already present, the images will not be flushed on update. However, if you delete that effect (I'm not talking about deleting the image style - delete the effect within the particular image style) and create a new one, the images will be flushed on update.
There is another, easier way. It's more a replacement than update, but it works fine. You can create a new image style based on the old one, but with new features (image actions) you wish. Then delete the old style; on the deletion confirmation page, you will find a drop list with available image styles, which you can use to replace the old one. This is a standard image style replacement function, I assume.