How can I change the CloudFlare's DNS servers address and use another one? I simply don't like the random word in one of the two addresses.
There is no way to change Cloudflare's DNS server addresses.
The servers are chosen per account, meaning that all of your servers will be given the same DNS addresses when added to that account.
Perhaps you'll get different DNS addresses if you'll delete your account and recreate it.
With that being said, there is absolutely no rational reason to spend any time about changing a word no one will ever see besides the one who configures the DNS settings for a new server.