After getting EV1 Server, before proceeding to configuring your site, you need to update all packages to newest one, including Plesk.
Then, you need to ask for additional IP from EV1 for your server. After receiving it, you need to configure you server with new IP.
Then you need to register your name servers to your IPs and then you need to re-delegate at DNS registrar new Name Servers for you domain.
Also, it is good thing to additionaly re-configure DNS template settings on Plesk Server pages.
And, make firewall as step number 0.
Good luck