You can use the Environment tab of the Project Settings dialog to add, modify, and delete environment variables.
To add an environment variable for the current project:
The Variable and Value fields below the Environment variables list are cleared.
To change the value of an existing environment variable, select the variable in the Environment variables list, then make the necessary changes in the Value field. When you are finished, click Set to save your changes.
To remove an environment variable, select the variable from the Environment Variables list and click Delete (the second of the three buttons in the top, right portion of the Environment tab).