You can change the thumbnail dimensions in Gallery Options > Inage Options then you can rebuild the existing thumbnails under Gallery Rebuilds > Rebuild Media Thumbnails
im not sure if you understand me sorry for my bad english
for example i have the first attachment the photo that im trying to upload which is wooden door and after uploading it show in anther attachment the image get cropping and it not show complete photo so i try to change a few setting in the gallery options and rebuild i did not see anything that change almost same ..
so can you tell me what exactly setting that i need to change ? or maybe that setting can't do what i need ?