Constituents can be removed from an email list from the Contacts page in the Email Marketing module.  You can use the edit icon to unsubscribe them or use the trashcan icon to delete them from a list.

They can be removed from a list one at a time by opening the constituent's record and clicking the "X" next to the email list name and then clicking Save to save the changes. 

Groups of constituents can be removed from email lists using Batch Update in the Actions menu.  Filter your grid to show the group of constituents you wish to remove from an email list. From the Actions menu, select Batch Update Records.  At Email List, select the checkbox to remove the email list from the entries and select the email list to remove them from. Click on Update at the bottom of the window to complete the action.