You can delete users that are no longer needed of your own accord. To do this, go to "Settings - Packages / licences / users" -> "manage user". Hover your mouse over the desired user. The drop-down menu "Actions" appears on the right-hand side. Choose the action "Delete" and then conform that the desired user can be deleted.
In a second step, under "Settings - Packages / add-ons / users" -> "Packages & licenses", select the licenses that are no longer required and finalize the order process. Alternatively, you can select the license directly after deleting the user under "Settings - Packages / add-ons / users" -> "User" -> "Cancel license", as depicted below.
Please note that, due to the 30-day notice period, additional user licenses that have been canceled will be charged until the end of the following month. Example: License is canceled on June 15; will be subject to charge until July 31.