I just updated an old laptop from FC21 to FC23 with DNF system upgrade,  It went very well and my daughter did not miss a beat with her reading MyOn or playing with TuxPaint.

Something like this...

# dnf update
# dnf install dnf-plugin-system-upgrade
# dnf system-upgrade download --refresh --releasever=23
# dnf system-upgrade reboot

I hope to update to FC24 next month...