This Excel Macro will go through all the cells in column A, find the last cell that has data in it, and then delete every other row in that data range.

To Delete Odd Rows

Sub Delete_Odd()

 Application.ScreenUpdating = False
lr = Cells(ActiveSheet.Rows.Count, 1).End(xlUp).Row

If lr Mod 2 = 0 Then
lr = lr - 1
End If

For i = lr To 1 Step -2
    Rows(i & ":" & i).Delete Shift:=xlUp    
Next i

 Application.ScreenUpdating = True

End Sub

To Delete Even Rows

Sub Delete_Even()

 Application.ScreenUpdating = False
lr = Cells(ActiveSheet.Rows.Count, 1).End(xlUp).Row

If lr Mod 2 = 0 Then
Else
lr = lr - 1
End If

For i = lr To 1 Step -2
    Rows(i & ":" & i).Delete Shift:=xlUp    
Next i

  Application.ScreenUpdating = True

End Sub

Posted by Excel Instructor:
https://www.chicagocomputerclasses.com/excel-classes/