You can always use a function to determine if the row is odd or even, off the top of my head you want to look up the MOD function which returns the remainder from a division. If you mod your row number with 2 and there is a remainder of 1, then the number is odd, if the result is 0 then the number is even.
Would also recommend not deleting the records but sending them to a separate dataset so as to be able to report on/check the results.