Can you define "best way" ?
You can use USBasp or any other programmer suitable for this uC, or as additional solution you can use bootloader.
With USBasp you can use :
AVRDUDE supports USBasp since version 5.2.
BASCOM-AVR supports USBasp since version 1.11.9.6.
Khazama AVR Programmer is a Windows XP/Vista GUI application for USBasp and avrdude.
eXtreme Burner - AVR is a Windows GUI Software for USBasp based USB AVR programmers.
USBasp project page
https://www.fischl.de/usbasp/
Best regards,
Peter