Help!: Change size options from Drop Down Menu to Buttons

I would like to change my drop down size options to be just the sizes above the add to cart button. I am on the Shopify Simple Theme.

https://shop.altashop.ca/collections/latest-arrivals/products/tiger-fleece-robe-men-reigning-champ-light-grey

to something like this:

Thanks for taking the time to read this!

Best,
Noel [email removed] Alta

To achieve this , login to shopify admin->customize->product page In sidebar theme setting and variant selection options.

Unfortunately, I don’t have that as an option in my theme customization settings. I have just “PAGE LAYOUT” and " SHOW AN EXTRA TAB OF INFO ON THE PRODUCT PAGE"

Thanks though!

Noel