OpenWrt will provide additional functions for the network (for example, you just want to use the Wi-Fi network it provides, or the device is a NAS serving files over the network, or a mini-server offering whatever other service).
Command line instructions to make the same we just did with Luci webinterface above, see above for more detailed explanation of the steps:
uci set network.lan.ipaddr='new-ip-address' and press Return
uci set network.lan.gateway='your-gateway-address' and press Return
uci set network.lan.dns='dns-address-here' and press Return
uci commit && service network restart(this will save the changes and restart network interfaces)