On the Quick Edit Window for your spec, you will see fields to edit the Specification Display Name, Brand Display Name, and Brand Display URL. Keep in mind that these changes will only customize the display information in this project and doesn’t affect or modify the original/source specification information.
If you're more interested in swapping the product's brand and/or model, maybe our Swap feature is a better fit for your workflow. Read more about it in this article: "How do I swap out one product for another in my project?".