Resize vs compress — not the same
Resizing changes how many pixels the image has — its actual width and height. Compressing keeps the dimensions but lowers the file size. Often you want both: resize to the dimensions you need first, and the file usually gets smaller as a result.
Keep the proportions
The most common mistake is stretching an image by changing width and height independently, which makes faces and objects look squashed. Locking the aspect ratio means you set one dimension and the other follows automatically, so the photo never distorts.
Done in your browser
Open the Resize Image tool, add your photo, type the width or height you need, and download. Nothing is uploaded — the resizing happens on your own device, so it works even offline once the page has loaded.