There is detailed article on how to configure different authentication modes in Team City.

But it lacks some information…

Let consider the following example:

1. You setup Team City
2. Configured Project in it
3. All went fine and now you need to configure user access
4. So you switched Team City to Windows Authentication
5. Now you can login with you Domain credentials, but you can’t give administrator rights to any user since you don’t have administrator yet

So I found the following workaround:

1. Login using Default Authentication Mode as Administrator in the Browser #1
2. Switch Authentication Mode to Windows Authentication
3. Login in as a Windows Domain User in the Browser #2
4. In the Browser #1 open Users and Groups
5. You will see newly created user account for Windows Domain User logged in using Browser #2
6. You can select this account and give it administrative rights