Once you’ve requested your license from WHMCS, you may download it by logging into your WHMCS client area at http://www.whmcs.com/members and following these steps:
Click on the My Licenses & Services link
Select one of your active license keys to view its details
Choose the latest stable version to download from the downloads listed at the bottom of the page
Follow these steps to install WHMCS:
Step 1: Upload the WHMCS Files
Unzip the contents of the compressed (zip) file to a folder on your computer
Rename the file configuration.php.new to configuration.php
Upload the entire whmcs folder to your website – if you experience problems, try uploading in binary mode
Next you may rename the folder to whatever you prefer (billing, clients, etc…)
Change the permissions for configuration.php to be 755 (CHMOD 755).
Step 2: Create the Database
Login to your cPanel for the domain you are installing WHMCS on (typically http://yourdomain.com/cpanel) to setup a database for WHMCS.
Click on “MySQL Databases” in the Databases section.
Enter a database name and click “Create Database” then click “Go Back” to return to the MySQL Databases page. (We suggest calling it whmcs but you may call it whatever you desire.)
Create a user for the database by entering a username and a password twice in the Add New User section and clicking “Create User.” Be sure to remember or write down the username and password because you will need them for a later step. Click on “Go Back” to return to the MySQL Databases page.
To add the user you just created to the database you just created, select the database and user from the dropdown lists, and click “Add.”
Check the box for “All Privileges” and then click “Make Changes.”
Step 3: Run the Installation Script
Visit the installation script at http://www.yourdomain.com/whmcs/install/install.php to run the installation process. (Replace “whmcs” with the directory you placed WHMCS in.)
Follow the instructions on the screen to install, which will involve setting the database, entering your license key and setting up your primary admin account
When completed, delete the installation folder “install” from your web server and CHMOD the configuration.php file back to 644.
Congratulations! WHMCS is now setup.