I want to update table using looping cursors

DECLARE @AccountID INT  -- Declaring a variable for holding Account id
DECLARE @getAccountID CURSOR -- Declaring Cureser
--Initializing Cursor 
SET @getAccountID = CURSOR FOR 
SELECT Account_ID
FROM Accounts
--Opening Cursor
OPEN @getAccountID
--Fetching First Value
FETCH NEXT
--Assigning selected value into Variable
FROM @getAccountID INTO @AccountID
--Checking Fetching Status(@@FETCH_STATUS this return the last fetch status
--  0  - The FETCH statement was successful.
-- -1 - The FETCH statement failed or the row was beyond the result set.
-- -2 - The row fetched is missing.)and starting while loop
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT @AccountID -- Printing AccountId. Here you can write your code.
--Fetching Next value
FETCH NEXT
FROM @getAccountID INTO @AccountID
END
--Closing Cursor
CLOSE @getAccountID
--Releasing Cursor
DEALLOCATE @getAccountID

update Table1  set serialnum = b.row1 from  Table1 as a inner JOIN
 (select itemcode,ROW_NUMBER() OVER(PARTITION BY icode  ORDER BY icode DESC) as row1   from Table1) as b
 on a.itemcode = b.itemcode