the openwrt-brcm2708-bcm2710-rpi-3-ext4-sdcard one is the controller/OS.
make sure you have the current and previous one handy as the new speed might not be what you want.
openwrt-brcm2708-bcm2710-rpi-3-ext4-sdcard this is sd card image, i want to upgrade working system without flash image to sd card.