Picture resolution problem

I am still very, very new at this wordpress thing and computers in general so I apologize in advance for the probable idiocy of this question.

I am having trouble adjusting the resolution of uploaded images on my site. The images I am uploading are more that large enough to fill out the fields I want but they are still getting blurry and I am not sure how to fix it. I have tried all kinds of different dimensions and they do not improve the quality of the images.

What am I doing wrong?