Hello @MehdiK9,
You should be able to view the contacts in a list and select them by clicking in the box to the left of their name. From there you can delete contacts by using the delete button in the dark gray bar at the top of the page. Please note you will need to delete per page, and cannot delete across multiple pages at once.
Another thing that might help, is if you have a list of the contacts that you would like to delete you can add them to their own list or tag. This way you could select all of the contacts in that list/tag and delete them from the account at once instead of having to check off each contact.
