The servers themselves will open late tonight.
In order to participate in the test using the Wargaming.net Game Center, use this link.
The Wargaming.net Game Center will download all the additional data
Size for download (SD): 671.75 MB
Size for installation on a computer (SD): 1.14 GB
Size for download (HD): 993.22 MB
Size for installation on a computer (HD): 1.68 GB