How do you start again on Pokemon White

To start a new game on Pokemon White and be able to save, first delete your old save file by pressing the up, select, and B buttons simultaneously while at the title screen. If this is done, the older save file cannot be recovered and everything in it is lost, but a new game can be started. Note that this method should also work for the other Pokemon games on the DS (though the button combination may be different)
Starting a new game without deleting the first save file is possible, but when that is done saving the new game is impossible.