Images on product page

When clicking the product images on my product page these are opened full screen and the user is supposed to hit the ‘go back’ button in order to return to the page.
I would like the images to appear as a overlay on the product page where the user is able to scroll between the different product images.

Here is a link to the product page: https://www.myacai.dk/produkt/oekologisk-acai-pulver/

Thank you in advance.

/Adil