On the tab there are combo boxes by which you can change:
If the Constrain proportions box is marked, in changing image sizes proportions will be kept.
As a result of choosing negative values the image will be smoothed.
JPEG compression is used. Image file size. in kilobytes, is displayed.
After selecting coefficient of change, click the Apply button.
You can apply the same filter many times.
Brightness and Contrast can be changed on the Histogram tab.