Download see:

This upgrade was also my first test of fedup, the Fedora Upgrade Tool (for my desktop, I only do installation, as I keep the various versions in multi-boot).

Upgrade: OK, a bit long, but mostly because of >3200 installed packages. I should have done some cleanup before.

To resume, on F18:

# yum install fedup
# fedup --network 20

After the packages download phase, the system is upgraded during first reboot, when on F20:

# yum check all
# yum distribution-synchronization
# package-cleanup --cleandupes
# package-cleanup --problems
# package-cleanup --orphan

No problem detected furing all the check operations.