I found the pics in /shoptest/images/styler/
In /yourshop/images/styler/ folder you should find the pic you are looking for. Download it and replace it with a pic the same size, and named the same. Then upload the new pic to the same directory. When you preview your shop the new pic will show.
Every time you publish your shop you will need to do this. Or buy the SCDP program and you can replace it for good.
Let me know if you still need help.
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