Changing Icons

[dcg234]

I'm trying to change icons using this website- interfacelift.com

The files are .sit files, and I have opened them, but I can't get the icons to be changed. I am trying to copy and paste to the new icon in to the "get info" window (I am clicking the icon and then edit-paste), but instead I'm getting a white icon that say "ICNS". I was trying with different image files such as JPG, Unix Executable File, .icns

What is wrong? I'm using the newest OSX

 

[6string]

see this

 

[dcg234]

OK thanks,
I'm having a weird problem right now-
If I change the icon to a different one, it looks like I can't change it for any other icon.
For example- if I copy-paste "icon a" to the folder, when I want to copy paste "icon b" to the same folder it would paste "icon a" instead, even if I change the icon to the default before trying to paste "icon b".

Are you experiencing the same problem? Is there any way around it?