Animated gif resizer
You can also use: http://ezgif.com/resize?url=http://link/to/image.gif
(Please be patient, resizing may take some time, depending on file size and resize method)
* GIF animation resizing is tricky, and you will probably have to choose between smaller file size or better quality.
Some gifs may require "coalesce" option (removes all optimizations from frames) if other methods fail and output image is flickering or has strange artifacts, but it may significantly increase file size and is very slow.
Try different methods if you are not satisfied with the result.
Gifsicle is usually the fastest tool and produces smaller files, but is designed for speed, not quality.