Assigning images to combinations

[mjinkjet]

Hi,  we are new to Prestashop and have a clean install of 1.7.5.2 with the classic theme that comes with it and stock management disabled. The only non Prestashop module installed is a paid for PayPal module. The problem we have is that we have created a new product, added two images to it and generated a combination with two values " White" and "Cream" but upon generation it immediately assigns the default image to both combinations with no way of us changing it.What we are trying to do is no different from the PS demo page which has 2 T-shirts where you can white or grey. From the PS manual and researching there should a popup screen which let us assign our images to the different combinations But this is not appearing. We have tried several things like clearing all caches, forcing template change and changing the attribute separator ('-' to ',' and back again) but nothing seems to work. Does anyone what we can try next? thanks.