1. Add all the images
Choose as many JPG, PNG or WebP files as you need.
2. Pixels or percent
Set an exact width, or a percentage such as 50%, for every image.
3. Compress if needed
For the web, run the resized files through Compress image to cut the size further.
Questions
Are the images uploaded?
No. Resizing happens on your device.
Related: Convert iPhone photos (HEIC) to JPG · Make images smaller for the web