Right click My computer and click Properties. System Properties window would open.
Click on Advanced tab.
Click on Environment Variables tab. Environment Variables window would be opened.
Scroll down the system variables to highlight path and click edit button. Edits system variable would be opened.
Add or modify the path lines with the paths you wish the computer to access. Each different directory is separated with a semicolon as shown below. C:Program Files;C:WinntSystem32
Click Ok. Click Ok on environment variable window. Click Ok on System Properties window.
Now to verify the paths set, open the command prompt by going to Start -> Run.