Upgrade via DNF into the alturnative Root
  http://dnf.readthedocs.io/en/latest/command_ref.html?highlight=installroot

  /dev/sda1   -- current root partition (FC22)
  /dev/sda2   -- new root partition (to install - FC24)

    # Clear the new root partition
    umount /mnt/alt
    mkfs.xfs /dev/sda2
    mount /mnt/alt

    # Information about that partition
    dnf --installroot=/mnt/alt grouplist
    dnf --installroot=/mnt/alt list installed

    # set server release version for the new root partition
    dnf --installroot=/mnt/alt --releasever=24 --nogpgcheck \
        install system-release

    # Install Base Environment
    dnf --installroot=/mnt/alt --nogpgcheck \
        groupinstall 'Fedora Workstation'

    dnf --installroot=/mnt/alt --nogpgcheck install kernel
    dnf --installroot=/mnt/alt --nogpgcheck install grub2

    # set disk devices -- swap root partition mount points
    cp -p /etc/fstab /mnt/alt/etc/fstab
    vi /mnt/alt/etc/fstab

    # set initial host information
    vi /mnt/alt/etc/shadow
      :1r !head -1 /etc/shadow
      :1d
    grep ^anthony: /etc/passwd >>/mnt/alt/etc/passwd
    grep ^anthony: /etc/shadow >>/mnt/alt/etc/shadow
    cp -p /etc/hostname /mnt/alt/etc/hostname
    cp -p /etc/ssh/ssh_host_* /mnt/alt/etc/ssh

  Set up Boot of new OS in grub

    # Is new OS visible?
    os-prober
    linux-boot-prober /dev/sda2

    # Add to grub boot menu on current OS /boot partition
    cp /etc/default/grub /mnt/alt/etc/default/grub
    grub2-mkconfig -o /boot/grub2/grub.cfg
    grub2-install /dev/sda

    # Setup grub boot on other root partition (mounted)
    grub2-mkconfig -o /mnt/alt/boot/grub2/grub.cfg
    #grub2-install --root-directory=/mnt/alt /dev/sda

    # List entrys and the menu numbers
    sed -e '/^menuentry/!d' -e "s/[^']*\('[^']*'\).*/\1/" \
           /boot/grub2/grub.cfg | cat -n

    # reboot to new OS (menu 5 from above) (once only)
    grub2-reboot 5       # <-- simple    vs  ,--verbose
    grub2-reboot 'Fedora release 24 (Twenty Four) (on /dev/sda2)'
    grub2-editenv list   # what is loaded on next reboot
    reboot

You can now install software and configuration as normal.
The old system is still available from /dev/sda1