Just click on the link. Then scroll to the bottom of the page and click the red button that says "Launch resizer." You will need to have the image downloaded
on your computer.

You will then browse your computer and upload the image.

You choose the size you want (probably 75% of the original size will work) and click 'Resize.'

Once this is done, you will then download the resized image to your computer. You can them upload it to an image host and use the link for your signature picture.

There are many free image hosts online. I use Image hosting, free photo sharing & video sharing at Photobucket.

PS: not knowing how to do something does not equal stupidity.