Open the certificate page from your profile and find a pencil button in the upper right corner. If you click it, you will be able to change your first and last name. Please be careful, you can change the names only once!
If Method 1 has already been used or did not work for you for some reasons, or if you need to change data in several certificates, send us the link to the certificate as well as your correct full name to https://support.stepik.org/hc/ru/requests/new.
In both methods you have to set your right first and last name in your profile in order for certificates to come to the right name from then. Please make sure that you set the correct name in your profile to begin with so there will not be such problems.