make image popup larger

I have several thumbnails on my main page set to popup. But the popup image is a flyer and too too small to read. I'd Iike it to open to a large scrollable image How do I make it bigger? If this is the wrong place to ask can you point me in the right direction. I've looked through the WIX support topics but can't even find a category to choose. When I search for public communities to ask this question, it always returns WIX forum app info. Thanks.