Minehut allows you to change your server's name after you've already initially selected one. Don't worry, it's free. Your server name is used in the IP of your server, so choose a good one.
To rename your server, go to your Server Dashboard:
Edit Server / Appearance
Simply click Change Name and type in your desired name. Server names must length between 3 and 10 characters and must contain only letters and numbers. If a server name is taken, then someone is already using that name, so you'll have to pick a different one.