Resizing images entirely in your browser
Choose an image, adjust the width and height (locked to the original aspect ratio by default, so your image does not stretch), and click resize. The resizing happens using your browser's own canvas engine - nothing is uploaded to a server, so your image never leaves your device. Download the result as a PNG once you are happy with the size.
Why the aspect ratio lock exists by default
Changing width and height independently without preserving the original ratio stretches or squashes the image, which is rarely what anyone actually wants - the lock keeps both dimensions proportional automatically as you adjust either one, so the resized image looks like a smaller or larger version of the original rather than a distorted one. Uncheck it only when you deliberately need a different aspect ratio.
Why file size usually drops along with dimensions
A smaller image generally has a smaller file size, since there are simply fewer pixels to store - but dimension reduction and compression quality are two separate levers. If file size specifically (not just dimensions) is your goal, pairing this with a dedicated image-compression tool that controls quality directly gives more predictable control over the final size.
Enlarging versus shrinking
Shrinking an image preserves quality well, since the browser is simply discarding detail that's no longer needed at the smaller size. Enlarging works differently - the browser has to invent pixels that were never in the original, which is why an enlarged image typically looks softer or slightly blurry compared to a true higher-resolution original.