Kai-Nguyen Thank you very much for your help.
For anyone interested in a similar solution here are all the steps I took:
This solution will create 3 displays for your catalog depending on screen width
3 products per row above 950px screen width;
2 products per row below 950px screen width;
1 product per row under 750px screen width;
01. DISPLAY 3 PRODUCTS PER ROW ON WIDER SCREES
Simply select 3 products per row as a default.
(On your shop’s dashboard, click the “Customize” button on your theme, go to your catalog page, and from the menu on the left select “Collection Pages”, on the menu on the right, under “Layout” select “Grid”, and under “Products per row (grid only)” select “3”).
02. CHANGE THE CATALOG PAGE WIDTH
Add this code to the bottom of your theme.css file
.page-width#Collection { width: 100%; max-width: 1500px;}
03. CHANGE PRODUCT’S IMAGE SIZE
Place the following code at the bottom of your theme.css file:
.grid-view-item__image-wrapper {
max-width: 500px !important;
max-height: 500px !important;
}
#Collection .grid-view-item__image {
max-width: 500px !important;
max-height: 500px !important;
}
04. SHOW 2 PRODUCT PER ROW IF THE SCREEN WIDTH IS UNDER 950px.
Place the following code at the bottom of your theme.css file:
@media screen and (max-width: 950px) and (min-width: 750px) {
#Collection .grid__item--collection-template {
width: 50%;
clear: none;
}
}
05. SHOW 1 PRODUCT PER ROW IF THE SCREEN WIDTH IS UNDER 750px.
Open “collection-template.liquid” under “Sections”;
On Line 131, change all “small–one-half” to “small–one-one” as shown below.
<div class="page-width" id="Collection">
{% if section.settings.layout == 'grid' %}
{% case section.settings.grid %}
{% when 2 %}
{%- assign grid_item_width = 'medium-up--one-half' -%}
{% when 3 %}
{%- assign grid_item_width = 'small--one-one medium-up--one-third' -%}
{% when 4 %}
{%- assign grid_item_width = 'small--one-one medium-up--one-quarter' -%}
{% when 5 %}
{%- assign grid_item_width = 'small--one-one medium-up--one-fifth' -%}
{% endcase %}
That’s it.