Environmental Variables on Windows 7 can be changed either by using the Control Panel –> Advanced System Settings or Control Panel –> User Accounts.
Using Advanced System Settings
Click on the Start Menu –> Control Panel
Select System and Security
Click on the Advanced System Settings available on the left hand side.
This would launch the Advanced System settings window with the option for changing Environment Variables
Using User Accounts
Click on the Start Menu –> User Icon
Click on the Change my environment variables to launch the Environment Variables window