So like I remember @Chronos did a really nice tool to converting the spritesheet format. Even if his tutorial is already simple I did a video of it to give more visibility to his software:
http://www.ascensiongamedev.com/resources/filehost/54d36038dc12632bf4ab21f84ee78e70.mp4
I take not credit for it, like I already said Chonos is tre creator of this tool, thank him not me.