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 selected resize method)
Online image resizer
Ezgif's online image resizer will resize, crop, or flip any images, and particularly animated gifs, with the same quality and speed as professional software, without the need to buy and install anything.
GIF animation resizing is sometimes tricky, and you will probably have to choose between a smaller file size or image quality.
Some gifs may require a "coalesce" option (which 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 resize 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.