Variants configuration lines retain their original order from when you first added them, according to the SKU starting each line. When you first configure Variants for a product, the config lines get added to our database as-is, in the same order you provided them, so subsequent changes just get applied for each existing SKU's entry in the database where it already is, and any new lines would get added at the bottom. Viewing an existing product's Variants configuration just reads off those lines from the database as-is, in the same order the database already has them stored.
In order to change the sorting order of Variants lines, you need to remove all the existing lines and then re-add them in the order you prefer, like so:
- Go to Seller Admin > Manage Products > View/Edit/Delete Products;
- Select your product and click View/Edit Product;
- Select all of its existing Variants configuration lines and use your computer's Cut command to copy and remove them;
- Optional: Paste the configuration lines into a separate plaintext file for editing/safekeeping -- e.g., using Notepad (Windows) or TextEdit (Mac, using plain text mode);
- Un-tick Variants affecting item SKU/price/weight/stock;
- Click Submit;
- Click Back to Product;
- Re-tick Variants affecting item SKU/price/weight/stock;
- Paste the Variants configuration lines back in, then rearrange them into the order you want (or you may prefer to rearrange them in that plaintext file from Step 4, then copy-paste the lines from there);
- Click Submit.