To delete a specific subscriber: Visit the audience tab at the top of the navbar and click on subscribers. Search the desired subscriber email you would like to delete. Click on their email. You’ll find a drop down arrow next to the “Unsubscribe” button with an option to delete the user as shown below.
If you’d like to bulk delete a group of users, you can go to the audience tab at the top of the navbar and click on segmentation.
Create a segment for the users you want to delete. Once the segment is created, revisit the segment and find the unsubscribe drop down menu as shown below and you should be able to delete the group of subscribers.