Microsoft keeps messing with this location on each release of Windows, so here are the approximate steps
1.Start the Control Panel
2.Click on "System and Security" then "System" then "Advanced System Settings". You're trying to get to the Advanced tab in the System Properties dialog.
3.Click on the "Environment Variables..." button.
4.Under the System Variables panel, click "New..."
5.In the Variable Name text field enter the environment variable, for example, lightmap_LICENSE
6.In the Variable Value text field enter the value you wish to set. For example, C:\Shared\lightmap\licenses\hdrlightstudio.lic