The export settings are available through the export menu:
Small: 1024 px on the longest side
Medium: 2048 px on the longest side
Large: 3072 px on the longest side
Original: The exported image is sized to the same size as the original source image (up to a maximum of 4096 pixels on the longest side).
Max: Upscales the image to 4096 pixels on the longest side, regardless of the original image size.