Update all rows but with limited number at a time
I would set up a WHILE loop similar to the following example:

set nocount on
IF OBJECT_ID('tempdb..#TableToUpdate') IS NOT NULL
    drop table #TableToUpdate
create table #TableToUpdate (KeyColumn int IDENTITY(1,1) NOT NULL,OriginalColumn int, NewColumn int)
go
insert into #TableToUpdate(OriginalColumn,NewColumn) values(1,1)
go 105

declare @RowsInTable int
declare @BeginRange int = 0
Declare @EndRange int = 0
Declare @Increment int = 10
set @RowsInTable=(select count(*) from #TableToUpdate)

while @EndRange &lt; @RowsInTable
begin

set @EndRange += @Increment

print 'updating ranges from ' + convert(varchar(100),@BeginRange) + ' to ' + convert(varchar(100),@EndRange)

update #TableToUpdate
 set NewColumn = OriginalColumn
 where KeyColumn between @BeginRange and @EndRange

set @BeginRange = @EndRange

end
GO