how to acces all drives on my ftp server

i run an ftp server so i can access my files from anywhere that has an internet connection.
i use serv-u ftp to run my server.
i have 3 hard drives but serv-u only lets me access 1 hard drive on an account.
does anybody know how i can make it let me access all of them from 1 account?
i've added more paths into the directory access but that doesnt work.