Thank you so much for your question. The size of google Adsense is 728*90 and have other sizes too. But the size you mentioned above is not the google adsense size. If you want to add your own image for advertisement there, you can make the image as your needed size and put it there. The original size will appeared there. You can try on free version of theme to add the Ad image as your need size. But, there are lots of additional options on Premium version of themes.