Step 1: On the administrator dashboard, click Invitations.
Step 2: Select the trash-can icon on the top right-hand side of your screen.
Step 3: Select all the invitations you wish to remove. The selected invitations will have a red border.
Step 4: Click the "tick" icon on the right-hand side of your screen. (If you'd like to cancel this process, click the "cross" icon.)