If it's classed as a "major" fault that essentially renders it unusable, the customer gets to choose the remedy, not the retailer.

This is usually so the customer can get their money back for a shit product, but there's nothing stopping them from a replacement.

Umart's claim that it's "an upgrade" doesn't hold much weight. If you buy X gigabytes of ram and it fails and you want a replacement with the same X gigabytes of ram, that's not an upgrade. It's restoring the status quo of the original purchase where they got a physical quantity of a product.