Can anyone tell me how to hack a ftp?

i wanna add a user name(with pswd) so that i can have my own account.

Well, if you just wanna get in, you can find out the server version by connecting and checking out the banner, then look for an exploit somewhere. Or you can try brute forcing an account. To get your own account, you could probably best achieve that by social engineering, since very few servers allow you to add users from the server (the program) itself. You'll have to change some config files on the machine. So you could either try and get into the server and edit the file yourself, or social engineer the place into adding an account for you.

Does that mean it would be hard for me to add my own account technically?

Yes, gaining access to an account via brute forcing is one thing, but creating one is what would have to be done with admin/root privelages over the service.