Hello @AmraD. We can certainly help you with this. Using the Advanced search, you can find contacts who are not on a list. Then, you will be able to delete these contacts.
First, go to the Advanced search under Contacts
Then, used the dropdowns to select "List" and "is blank". When you click the Search button, you will then have a list of all contacts who are not on any of your lists. From there, you can select these contacts and delete them.