How to change my minecraft skin in cracked minecraft?

I saw something saying go to bin and open minecraft.jar but when i try it says it's invalid or something can i have some help please?

You can't

I'm going to assume that you're using Mineshafter as your cracked Minecraft website. Just go to http://mineshafter.info/ Then sign in on the top right corner. Once you sign in, hover over your username and click settings. At the bottom of the page there should be a bow that says "Skin URL" Choose a skin from a link that looks like this: image
Or choose one from http://minecraftskins.com You can upload a skin there if you already have one. Put the skin url in the "Skin URL" box on Mineshafter and hit set. You now have a Minecraft skin on a cracked client.

Buy mc its only 27$ hope that help