- Go to "File" - "Batch Conversion/Rename".
- Work as "Batch conversion"
- Find the directory where your images are and click "Add all"
- Output format jpg, gif or png.
Check "Use advanced option" and click on the button "Advanced".
- Check RESIZE and choose "Set new size as percentage of original" (maybe 10%, it depends on the original file size)
Click OK to close the advanced dialog.
- Choose "Output directory for result files" (should be different directory than where the original files are)
- Click on "Start Batch"