Update records row by row using cursor in sql

How to loop through a table and update row by row using cursor in sql. ...basically looping through a table and updating record one by one in ms sql.

declare @cur1 cursor
declare @col1 varchar(10)
declare @col2 varchar(10)
declare @col3 varchar(10)
declare @col4 varchar(10)

set @cur1 = Cursor FOR SELECT column4,column1,column3 from myTable1

OPEN @cur1
FETCH NEXT FROM @cur1 into @col4, @col1, @col3
While @@FETCH_STATUS = 0
begin
select @col2=column2 from differentTable2 where someColumn=@col3

if @col2 is not null
begin
Update myTable1
set column2 = @col2
Where column4=@col4
end

FETCH NEXT FROM @cur1 into @col4, @col1, @col3
End
close cur1
deallocate cur1