WARNING: Before upgrading, you should backup the system first!!!
Disclaimer: This is just my experience. It is not guarantee the steps listed will work on your system.
Openwrt upgrade on x86 can be very tricky in the old days. However, it becomes an easy task starting from attitude adjustment (12.09) and onward.
The following lists the steps to upgrade to the latest snapshot (barrier breaker). You should change the image to be downloaded in step 4 for the desired version.
- Do a full system backup to avoid any lost. This is very import!!!
- login the system as root
- cd /tmp
- wget http://downloads.openwrt.org/snapshots/trunk/x86/openwrt-x86-generic-combined-ext4.img.gz
- sysupgrade -v /tmp/openwrt-x86-generic-combined-ext4.img.gz