The latest version:
1. Select “Options” -> Thumbnails -> Set your size -> Check the box “Ignore the aspect ratio, no portrait thumbnails”
2. Select “Manage Gallery” -> Select your gallery -> Check the “ID” box above the the images -> select “Create new thumbnails” from the dropdown and click apply. this will resize all of you existing thumbs in your gallery.
You can also skip step one and go directly to step two if you wish to only apply this once to a single gallery in your website
Aquim Media