There are several ways to remove a constituent from a list. They can be removed from a single list, all lists or unsubscribed from all emails.
To remove a constituent from one particular list or all lists, you can go to their profile page and click on the small "x" next to each email list to remove them from. You can remove them from just one or all lists in this manner, however they are not given an "unsubscribed" status in their primary email, which would prevent you from adding them to lists in the future.
You can also delete them from specific lists using the Contacts Page in the Email Marketing Module. Open the list and click the trashcan icon to delete them from the list. This does not delete the constituent, only removes them from that email list. You can also click on the edit icon to mark them as unsubscribed from that one list. It does not affect subscriptions to other lists.
If you need to remove a constituent from all lists AND mark their record as Unsubscribed so that they will not receive any future email marketing communications and cannot be added to any email lists, then go to the Contacts Page and click on ALL RECIPIENTS.
From the grid, search or filter the list to find the constituent and check the box under the "Unsubscribe" column. This will remove them from all lists, flag their record and change their email status to Unsubscribe.