Please upgrade your Yún - latest is 1.5.3

Please someone help. I'm trying to update the OpenWRT-Yun image on my Yun. I've tried the webpanel, but the reset button doesn't appear. I've tried the Terminal, but I really have no clue what I'm doing there. I followed the steps, but this is what I get:

root@Arduino545:~# run-sysupgrade /mt/sdal/openwrt-ar71xx-generic-yun-16M-squash
fs-sysupgrade.bin
cp: can't stat '/mt/sdal/openwrt-ar71xx-generic-yun-16M-squashfs-sysupgrade.bin': No such file or directory

I really want to get this Yun working. Please respond in terms that a general computer use would understand. Thanks so much!