As an Administrator, you can conclude classes on an individual basis by first navigating to the Classes tab on the left sidebar.

Select your desired class from the classes menu on the right side of the page.

Click the Conclude button at the bottom of the page.

As an Administrator, you also have the option to conclude every class in a term at once.  First, click the Terms tab on the left sidebar.

Navigate to your desired term through the Terms menu on the right side of the page.

Click the Conclude button to conclude all the classes belonging to that term.