How do I solve the problem with one of my pictures getting cut of in Gallery Slider

Hi I also have this huge problem where I cannot get the picture in the Gallery slider right.It shows only a part of the picture of my painting and I have tried everything, installed regenerate thumbnails, to change the thumbnail to show the part of the painting I prefer – resizing the image. Nothing helps. You can see what I mean on my webpage http://www.aj-kunst.dk in the gallery slider, it is the first picture where the heads of my birds are cut of . If it is not possible how do I then insert a different thumbnail picture in the post and get another (the whole painting) to show up when I click on the gallery slider picture? Hope somebody can help. I am not very familiar with programming and html so please – an easy guide :0) Thanks and once again…I love the Minimatica theme. Anitta