By default, a cleaned image keeps its original size (resolution) and aspect ratio. However, the scale item in the File menu enables you to change the resolution and aspect ratio. Note that this feature is only available for cleaned image.
The dialog window of "Scale image" is shown below.
The width and height in pixels of the original image are filled in automatically if "Keep settings" is not selected. You can adjust the width and height by entering new numbers. If you press "Enter" key after filling in either "Width" or "Height", the other box will be adjusted automatically using the aspect ratio of the original image. If you want to scale width and height independently, just fill in new numbers without pressing the "Enter" key. Once you are satisfied with the new size, just click OK and your image will be scaled accordingly. To keep your settings for next image, select "Keep settings".