Unfortunately, once a developer.ebay.com account is created, the Company Name field is set as a primary key for the account that can't be changed.
However; you can go to your developer.ebay.com account and change the Display Title for the RuName of interest as below:
1. Go to My Account page, login to developer.ebay.com if needed.
2. Click on the Configure Settings » link that associated with your Production key set so that you are redirected to the Home > Support > My Account > Application Settings page
3. Then click on the Customize the eBay User Consent Form » link to go to the Home > Support > My Account > Application Settings > Application Level Settings page
4. on the Manage Your RuNames section, click the Show Details » link
5. Update the Display Title for this RuName.