I believe I have the answer to your question. Click on the "Setting" tab. On that page you will find the following..... At the top is the "title" you gave your website. You can change it there if you misspelled you family name. Also at the bottom you will find: "Pick a unique address for your site". To the right of "address" is the name you used for your myHeritage website. If you misspelled your family name there you can change it as well.
I believe this only available to the site managers of your website.