Make sure you can ssh to the router by root
and type in the command:
cd /tmp
wget http://downloads.openwrt.org/snapshots/trunk/ar71xx/openwrt-ar71xx-generic-mw4530r-v1-squashfs-sysupgrade.bin
sysupgrade -v openwrt-ar71xx-generic-mw4530r-v1-squashfs-sysupgrade.bin