Can I resize without distorting the image?

Yes — leave the aspect-ratio lock on and set only the width or only the height. The other dimension is calculated for you, so the proportions are preserved exactly.

Can I make an image larger?

You can, but upscaling cannot invent detail that was not captured. Going beyond about 200% starts to look soft. If you need a genuinely larger image, re-export it from the original source at the size you need.

What size should I use for the web?

Match the largest size the image will actually be displayed at, then double it for high-density screens. A full-width hero on a 1440px layout wants roughly 2880px; a thumbnail shown at 300px wants 600px. Anything beyond that is bytes nobody sees.

Image Resizer

Set a new width and height in pixels, or scale by a percentage, and the resized image downloads immediately. Lock the aspect ratio to keep the proportions, or unlock it to stretch to an exact size. Resizing happens on a canvas in your browser — nothing is uploaded and nothing is queued.

Runs in your browser — nothing is uploaded

Questions

Can I resize without distorting the image?: Yes — leave the aspect-ratio lock on and set only the width or only the height. The other dimension is calculated for you, so the proportions are preserved exactly.
Can I make an image larger?: You can, but upscaling cannot invent detail that was not captured. Going beyond about 200% starts to look soft. If you need a genuinely larger image, re-export it from the original source at the size you need.
What size should I use for the web?: Match the largest size the image will actually be displayed at, then double it for high-density screens. A full-width hero on a 1440px layout wants roughly 2880px; a thumbnail shown at 300px wants 600px. Anything beyond that is bytes nobody sees.