Go to the Overview (Day or Week view), double click the class you want to cancel, click a gear button and choose 'Cancel This Class' option.
You may also click with a right mouse mutton on a class you want to cancel and choose 'Cancel This Class' option.

This way you will cancel a particular regular class. Other classes will stay unchanged.
Go to the Calendar or Today pane, tap on a class you want to cancel and tap 'Cancel This Class' button.

This way you will cancel a particular regular class. Other classes will stay unchanged.