How do I unload spritesheet?

I have a spritesheet (one png file with all the assets in it). But I don't know how to separate it into individual images.I searched a lot on internet but I didn't got my solution

And also the images are randomly scattered in the file

You'll want an image editing program to do so, like Photoshop, Gimp, or Paint.net.

Look up how to crop something in your program of choice.