Cropping removes the parts of a photo you don't want and is the right way to change its shape without stretching.
Step 1: Load your image
Open the Crop Image tool and drop in the photo.
Step 2: Set the crop area
Drag the crop box, or type an exact width, height and offset. For a fixed shape (1:1, 16:9), set the dimensions to match that ratio.
Step 3: Download
Cropping is lossless — the kept area is untouched. Want to split one image into several pieces instead? See how to split an image. Related: image aspect ratios.