To move or delete large numbers of addresses:

Select the group you want to move from or delete from.

Choose Edit > Find > Find Addresses...

Type or paste the email addresses you want to move or delete.

Click OK.
You can delete addresses from Direct Mail by selecting the address and pressing the delete key. Addresses can be moved by dragging them from the address list into a group (hold down the option key to copy, rather than move). If you are moving or deleting a large number of addresses, you may find the Find Addresses feature useful.
Select the group you want to move from or delete from.
Choose Edit > Find > Find Addresses...
Type or paste the email addresses you want to move or delete.
Click OK.
The addresses you searched for will appear in the Addresses tab. You can move or copy them from there (by dragging and dropping). To show all your addresses again, click the "X" in the search field at the top-right corner of the window.