To change the labor rates, open your project and click Project Details on the left nav bar.
In the overlay that appears, you will see all of your labor info under Labor Rates. In the left column, there are the four labor categories: Engineering, Installation, Management, and Programming. In the center column, there are each of the Labor Types that you have created for the selected category. In the right column, there are fields in which you can edit your labor rates.
Simply change the numbers in the rate column and click Update in the bottom of the overlay. This will apply your new rates to the project.
To find out how to edit your company-wide labor rates, click here.