Photoshop

[Picture source: http://www.dandeware.com/screenspace/img/resize.png]

Yes there are many automated GIF resizers available on the web, but the advantage of using Photoshop for this task includes having the best output quality with the least file size. Not to mention you may also do some enhancement such as changing the brightness or sharpness of each frame.

[Light Saber effect I created using Photoshop CS4]

This is the video tutorial, check out this guide for more detailed step by step explanation.

Get this book called 'Photoshop for Right Brainers'. It is the best photoshop book for beginners like myself.

[Light Saber effect I created using Photoshop CS4]

I wrote this guide as simple as possible so don't be afraid if you're a total photoshop beginner. I also created the video version if you prefer to learn via video.