If you are a developer or want to change some system paths in Windows 7, you need to know how to change the environment variables. Do so carefully, because you can break your system if you don’t know what you are doing.
1. StepOpen up the Control Panel
2. Step Click on System and Security
3. Step Click on the System link:
(The text “System” is a link)
4. Step In the sidebar click on “Advanced system settings”
5. Step Go to the tab Advanced. At the bottom you will find a button labeled Environment Variables:
6. Step Below system variables you will find for example the environment variable CLASSPATH. The CLASSPATH variables is often required for paths to PHP executables or similar (if you set up an Apache server locally).
Important: Keep in mind that environment variables are separated by a semi-colon.