How do I view and edit the code of my Prestashop site?

[Miju-friend]

Hello,

I would like to put a label on my products on the front page, telling customers if an item is sold out. I have read several threads on it, but since I am quite new to coding I don't know how to get to the actual editing.

Can anybody help me?
First on getting to the place where I can edit the code, and then where in the code I need to put in the

{if $product.quantity==0}
IMG HERE
{/if}

-part or whatever the right code might be.

I am using Prestashop 1.7 on https://miju-julepynt.dk.
Any feedback to the site in general is welcome.

Thank you :)
Ditte