I cannot update my psp 1000 from 5.00 m33-6 to 6.35 Pro-A Updater?

The psp model I'm using is PSP Phat or 1000. I downloaded 6.35 Pro-A Updater and I drag "635proupdate" folder to my PSP/GAME. After that, i disconnect usb connection and i went to game and i went to update 3.35 Pro-A updater. Then it said "This program requires 6.35". So I had no idea where to start off. plz provide a link include a tutorial if necessary.