You can drain & refill with engine off, but to fill to correct level you have to have engine running go trough all gears then put in park or N (with engine running) & fill it again , or you will be low on ATF at least couple quarts,

 

Yes, proper procedure is drain and refill cold, start engine, cycle through gears, and with engine still running crawl under and add fluid until a steady stream pours. Test drive, recheck again or the next day. Engine should be cold before starting the procedure though.