How do I change my icons?

I downloaded an icon pack.
I think they are all 256×256 PNG.
How do I change the pics of my icons for Win 7 x64 bit?
Answer #1
Step 1
http://i46.~ Disallowed image host. Please Report. ~/2m8455u.jpg
Step 2
http://i49.~ Disallowed image host. Please Report. ~/hwgyom.jpg
I hope this helped.
Answer #2
I don’t think you can put PNG as icons mate.
Only the format ICO’s.
Answer #3
Seems a bit lat but try http://converticon.com/