1. Download the plesk installer from their website.

wget http://autoinstall.plesk.com/plesk-installer

2. Change the permission to executable.

chmod +x plesk-installer

3. Run the script.

./plesk-installer

To start the installation or upgrade, press N and then press Enter.
To quit the installer, press Q and then press Enter.

—— IMPORTANT ——

* Before installing or upgrading Parallels products, be sure to back up your data.

* New installation of product(s) should be performed on clean servers only.
  Only the operating system with the networking option should be
  installed for new installations.
  Parallels will not be held liable for damages resulting from installation
  of products on a server with anything other than a fresh installation of the
  operating system for which the product installation was intended.

By using this Wizard you agree to the terms and conditions described at
http://www.parallels.com/en/company/terms/ and those of the Parallels Panel End User
License Agreement.

N) Next page;  Q) Cancel installing
Select an action [N]:N

Select product software source
===============================================================================

You can install products by using any of the following sources:

 * Local media
 * Official Parallels server
 * Other network site

Current settings:
 Install products from Parallels server
 Install required system packages from Parallels server
Store downloaded files in: /root/parallels

N) Next page; P) Go back;  Q) Cancel installing
S) Change source; T) Change target directory;
Select an action and press ENTER [N]:N

HTTP Proxy Setup
===============================================================================

If you are behind a firewall and use an HTTP proxy, you should specify the proxy server below.
If your proxy requires authentication, select “Use authentication”
and specify the username and password

Current settings:
 Do not use proxy.

N) Next page; P) Go back;  Q) Cancel installing;
S) Select proxy server; A) Use authentication;
Select the required action [N]:N

Select the desired products and their versions
===============================================================================

The following product versions are available:

1. [ ] Parallels Plesk Panel

N) Go to the next page; P) Go to the previous page; Q) Cancel installing
To select a version, type the respective number;
Select an action [N]:1

Select the desired products and their versions
===============================================================================

The following product versions are available:

1. [*] Parallels Plesk Panel
  2. (*) Parallels Plesk Panel 12.0.18
  3. ( ) Parallels Plesk Panel 11.5.30

N) Go to the next page; P) Go to the previous page; Q) Cancel installing
To select a version, type the respective number;
Select an action [N]:2

Would you like to help Parallels make better products by sending information
about installation, upgrade, and other problems? [Yes]: Yes

Select the installation type for Parallels Plesk Panel
===============================================================================

Installation types for the product:

 1. (*) Typical
       Install typically used components. Recommended for general use.

 2. ( ) Without DNS server
       Install typically used components without DNS server (BIND).

 3. ( ) Full
       Install all available components.

 4. ( ) Custom
       Custom components selection. Recommended only for experienced users.

N) Continue installation with selected type; P) Go the previous page; Q) Cancel installing;
L) View or change components marked for installation;
To select an installation type or choose another product, type the respective number;
Select an action [N]: N

Determining the amount of free disk space
===============================================================================

Following amount of diskpace required in directories:
/usr/local: 1200.00 Mb.
Total required: 1200.00 Mb, available 867684.00 Mb.

N) Next page; P) Go back; Q) Cancel installing
Select an action [N]: N

4. Once the installation is finish, you can now browse your new plesk server by typing your server IP to the browser.

https://<YourServerIP>:8443