When something is faulty

Reject, repair, refund.

The usual ladder

A short early window to reject for a full refund, then a right to repair or replacement, then a price reduction or refund if that fails.

Go to the seller, not the manufacturer.
After the first months the burden of proof often shifts to you.

Making the claim

Report the fault promptly in writing, keep the packaging and the receipt, and state whether you want repair, replacement or refund. Do not accept a credit note when a refund is due.