Age of Origins Guide presents when and why you should change your commander skills.
It costs 1000 gold each change but you can find items on discount in black market, privilege shop (800 gold) or distribution center for Aoz coins.
I recommend depending on your limitations to prioritize unlocking mobility recovery if you often log in and can kill zombies. The more mobility you get back to kill zombies per day, the more xp and good stuff you get, the faster you’ll level up and get more commander skills to use.
The war track is important to maximize dmg and other important stats but if you don’t fight often and you aren’t going to move into a higher reward tier with the stat increase, prioritize development track.