Ok, here's how to quickly extract a sprite.
You will need:
-Adobe Air and ShoeBox
-Lunapic Website to make your background transparent
-Spritesheet you want converted
Step 1. You want to clean your sprite sheet first from anything like borders, author graphics, mixed colors. I use paint as it's simple, easy, and I'm familiar with it.
Step 2. With Lunapic open, click on Browse under Edit a Pic, then select your Sprite Sheet.
Step 3. Click on Edit, then Transparent. It will bring up Make image background transparent. All you got to do is simply select the background color, and then go down the page and click Save on your computer
Step 4. Install Adobe Air, then install ShoeBox
Step 5. Open ShoeBox. Navigate to your folder where the converted image is and click and drag to Extract Sprites.
Step 6. You can go to the settings if you want to improve the sprite extracting. Borderline option improves it. You can click on each sprite and rename it, though don't press enter and click out when you are done. Simply click on Save and that will save all individual images in the same folder.
Alternative programs to use is Alfred Sprite Converter, though I prefer ShoeBox as it has additional features, and looks better.