1. Go to http://pixlr.com/editor/
2. Click 'Open image from computer' - locate and open the image you wish to resize.

3. Click on the Crop tool (top left icon) in the tools menu.

4. At the top of the page set the Constraint option to 'Output size'. Now you can set the width and height of the cropped image.

5. Set the width and height to the pixel dimensions you need

6. Now put your mouse over the image, click and drag your mouse to set the area of the image you want to be cropped.

7. Press Enter to confirm the crop or ESC to cancel it.
8. Once you've cropped the image, go to the file menu (top left), and click 'Save',

9. Make sure you save the cropped image with a unique name (so you don't overwrite the original image). The format should be JPEG for photos and GIF for logos. Set the quality between 60 and 80 for the best finish at the lowest file size.

9. Now upload the image to the your website.