1. Go to https://pixlr.com/editor/
2. Open the image from your computer
3. Go to Image - > Resize Image
4. Scale the image to the size you need. Be warned that resizing an image from small to large will distort the image quality. Click OK when you are content with the size of the image.
5. Go to File - > Save
6. Select your image format. If you save as a JPEG you need to see the quality of the image. Click OK to Save.
7. Use the resized image for your intended purpose on your website.