By default, variant values appear on the product details page in the order specified when you created the product type. You can override the default order for individual products.
To reorder variant values on the product details page:
On the Catalog tab, open the product whose variant values you want to reorder.
On the SKUs tab, click the Edit icon next to the name of the variant whose values you want to reorder.
Reorder the values and click Update or Save.