How to increase performance of UPDATE of ~ 50.000.000 entries
One more thing. If these tables are very larges even if you have good indexes, you should updates these tables rows in cycle, because the transaction log is growing every time and big transactions takes more times.

Example:

CREATE TABLE UpdateTable(id int IDENTITY(1,1), name varchar(200), namenew varchar(200))

INSERT INTO UpdateTable VALUES ('Old1','New2');
INSERT INTO UpdateTable VALUES ('Old2','New2');
go

SET NOCOUNT ON;
DECLARE @cnt INT = -1;

WHILE (@cnt&lt;&gt; 0)
BEGIN
    UPDATE TOP (1) UpdateTable
    SET NAME = namenew
    WHERE name &lt;&gt; namenew

    SET @cnt = @@ROWCOUNT;
 END    


You should change the top (1) to an acceptable value like 100000 or bigger you can measure it on your environment