opkg
Usage
Update package lists:
opkg update
Upgrade packages
To upgrade a group of packages, run opkg upgrade packagename1 packagename2. A list of upgradeable packages can be obtained with the opkg list-upgradable command. Since OpenWrt firmware stores the base system in a compressed read-only partition, any update to base system packages will be written in the read-write partition and therefore use more space than it would if it was just overwriting the older version in the compressed base system partition. It's recommended to check the available space in internal flash memory and the space requirements for updates of base system packages. Upgrading packages you installed should not have this issue as they are already in the read-write partition so the new one will overwrite the older one, although checking before upgrading never hurts. As a general rule of thumb, devices that have 8 MiB or more total flash size and no user-installed packages should not have space issues when updating base packages, and of course devices set up for Extroot won't have any space issue.
opkg upgrade <package>
Upgrade all installed packages
Mass upgrade of all packages is strongly discouraged. If you still want to proceed, set up Opkg extras or use the following one-liner:
opkg list-upgradable | cut -f 1 -d ' ' | xargs opkg upgrade
List All Installed Packages Sorted by Size
cd /tmp
wget https://openwrt.org/_export/code/user/vvkjndl/opkg-list-packages-sorted?codeblock=0
sh /tmp/opkg-list-packages-sorted\?codeblock=0