On any Allwebco template, the thumbnail and full sized images can be either vertical (portrait) or horizontal (landscape) and any size or shape that you would like. Most Allwebco templates you do not need to do any extra editing for this.
Editing the gallery image sizes
In any Allwebco template other than "Museum" style models you can simply edit the images in your template "gallery" folder to any size you would like. The template gallery pages should update with your new sizes and no other editing should be required. If your images still do not update here are some solutions:
Museum style templates
On Allwebco "Museum" style templates the frames are defined with CSS code. You can switch any one of them to horizontal or vertical with a fairly sample edit. Gallery 5 on any of these models is a vertical gallery if you would like to see a sample.