Go to the Resize on Upload section. Here you can specify what happens to all your images when they are uploaded.
Width and Height: Resizes the image file to your desired pixel format, without stretching or leaving a blank space.
Crop: Selecting the crop option will cut out an area of your image, from the middle, to the size of your selected width and height.
Quality: Determines the quality of the image. The field accepts a range from 0 to 100, with 0 being ‘lowest quality’, and 100 being ‘best quality’.*
*Higher quality means better looking images but also bigger file sizes (and potentially slower performance). Recommended for this field is 80.