Hi there lajos.andrejkovics,
Thank you for choosing Apple Support Communities!
It sounds as though you’re looking to change the name of your Mac computer. You’re in the right place, we’d be glad to assist in seeking a solution.
Below is a resource that can help. What happens when you click the "Edit" button below the computer's name?
Change your computer’s name or local hostname on Mac
If you’re instead looking to change the name of your macOS User account and home holder, this resource provides steps that can be used:
Change the name of your macOS user account and home folder
Have a great day!