Featured product image appears as circle – change to square

Hi there,

I have just installed my new theme – Rustik and trying to work my way around it.

One very annoying things is that my ecommerce shop featured image appears in a circle form. I’d like that to be a square.

Please help solving this, I am very desperate by now, could not find any sense making answers.. (do not know too much code)

Cheers,
K.