Batch resizingWhen an image is uploaded, several sizes of that image are created automatically. Most of these sizes can be resized gallery-wide using the batch resize tool.
Before batch resizing a particular size of image in a gallery, it's a good idea view them all first. This can be done by going to the Admin Panel > Image gallery (any one) > Images: View All.
This opens a new browser window that displays all the images in the gallery at a particular size. You can change this size by clicking the on Smallest, Thumbnail, Big or Biggest in the upper right corner.
To change all of the Thumbnail, Big, or Biggest size images in a gallery, you can do the following:
Go to the Admin Panel > Image gallery (with the images) > Advanced in the upper right corner.
Scroll down until you see Thumbnail Height, Big Image Width, Biggest Image Height.
Click on the image size you want resize, for example, Thumbnail Image Height. And set the new Thumbnail Image Height setting, for example, here. Then, click Regenerate images... and the images will begin resizing.
Once finished, click Save in the lower right corner of the pop-up. And, then click Save Changes at the bottom of the image gallery page.