首先检查服务器是否已经满足系统要求：
System Requirements
Most current web servers* with PHP & MySQL installed will be capable of running WHMCS.
The following table shows the minimum and recommended system requirements for running WHMCS 7.0 and later.
| Requirement | Minimum | Recommended |
|---|---|---|
| PHP Version | 5.6.0 | Latest 7.x Release |
| PHP Memory Limit | 64MB | 128MB** |
| PHP Database Extension | PDO | PDO |
| PHP Extensions | Curl with SSL GD2 Image Library JSON Support MBString XML |
Curl with SSL GD2 Image Library JSON Support MBString Iconv |
| MySQL Version | 5.1.0 | 5.5.x |
| MySQL Strict Mode | Disabled | Disabled |
| Ioncube Loaders | 5.0.21 for PHP 5.6 6.0.2 for PHP 7 |
The latest 5.x version for PHP 5.6 The latest 6.x version for PHP 7 |
WHMCS 6.x supports PHP 5.3.7 or later, including PHP 5.4, 5.5 and 5.6.
WHMCS 7.x supports PHP 5.6 and 7.x
While these are the minimum requirements, we strongly recommend using the latest available, stable releases of all software and extensions. Recommended suggestions are correct as at 2nd February 2016.
Looking for the requirements for the WHMCS 6.x series? Click here
* We validate WHMCS to run in Linux based environments running the Apache web server. Other environments such as Windows based configurations may experience compatibility issues and are not supported.
** Memory requirements vary depending upon the size and volume of activity in an installation. Your exact requirements may differ.
升级前备份所有文件和数据库。Before upgrading,you need backup all files and database.
将WHMCS 7所有文件覆盖到原安装文件夹，之后把旧的configuration.php配置文件覆盖现有文件,然后访问http://www.yourwebsite.com/installUpload the new files to your existing installation folder replacing any existing folders & files.Visit your WHMCS installation（Example:http://www.yourwebsite.com/install） and you should then be automatically redirected to the upgrade process. If you see a message saying WHMCS is not installed, this indicates you have overwritten the configuration.php file for your installation. Stop and restore that file from your backup before continuing.
如果提示你将MySQL Strict Mode从On修改为Off,数据库执行以下语句关闭严格模式.If you need setting MySQL Strict Mode is [Off]:
vi /etc/my.cnf
sql_mode=””
然后就完事了。