updating sql table where other tables match

hi guys,

I have the following statement:

This creates a new table putting together pieces of 2 tables where 2 conditions exist.

Now I that the table exists... the second time I run this I just want to update the values.
Can someone please help me change this query from a create new table... to update the existing table.

Appreciate it
thanks

SELECT 
	dbo.PositionsDB.Account_ID, dbo.PositionsDB.Position_ID, dbo.AccountsDB.Account_Number, 
	dbo.AccountsDB.Account_Description,	dbo.PositionsDB.COB_Date, dbo.PositionsDB.Qty_Net, 
	dbo.PositionsDB.Exchange, dbo.PositionsDB.Product, dbo.PositionsDB.Contract_Date, 
	dbo.PositionsDB.Option_Type, dbo.PositionsDB.Strike,
	dbo.PositionsDB.Settlement_Price
INTO dbo.DailyPositions_JEFF
FROM dbo.PositionsDB
INNER JOIN dbo.AccountsDB
ON dbo.PositionsDB.Account_ID = dbo.AccountsDB.Account_ID
WHERE dbo.AccountsDB.Client_ID = '418bb7b8-0180-4a5a-99f6-ce52e60e694f'
AND [COB_Date] = '20121219'