Simple terms.
1.... Goto Microsoft website, download the LATEST dashboard update, either put this downloaded file onto a USB pen drive, or burn it onto a BOOTABLE cd-rom
2... Put said USB drive in one of the USB ports in your 360, or if you've burnt it to a CD, then power on the Xbox, press eject, put the CD in, then switch OFF !
3... POWER ON, the 360, let the new DASHBOARD install onto your 360.
4... GET YOUR SHINY NEW UPDATED 360, RE_FLASHED, as it is now STOCK