I have tested this method on several machines, but if you have problems, please let me know. Always remember backup, before upgrade!
1. Before Upgrade
1.1 Backup Your Data
Before doing anything, do full system backup or backup at least your important data: documents, pictures, videos, config files, log files, databases etc. This is very important step, because if something goes wrong and you have to do fresh install, then you can easily restore your data.
2. Upgrade Fedora 27 to Fedora 28 using DNF
Following steps are mainly Fedora Server and command line users
2.1 Change root user
su - ## OR ## sudo -i
2.2 Update Fedora 27 Packages
Just make sure that you have all latest packages installed.
2.3 Reboot Your System
Just make sure that you are running latest kernel.
2.4 Install/Update dnf-plugin-system-upgrade package
It’s probably installed already.
dnf install dnf-plugin-system-upgrade --best
2.5 Start Upgrading Using DNF
dnf system-upgrade download --releasever=28
When this finish, check if there is any errors. You might need
options to get all packages downloaded.
2.6 Start (F27 to F28) Upgrade Process
dnf system-upgrade reboot
2.7 Grub 2 Menu Boot with Latest Kernel
2.8 Starting System Upgrade
2.9 dnf-plugin-system-upgrade Upgrading Fedora 27 to Fedora 28
3. Fedora 28 Screenshots
3.1 Fedora 28 GDM Login Screen
3.2 Fedora 28 Plain Desktop Gnome Shell 3.28.1
3.3 Fedora 28 and Gnome 3.28.1
4. Fedora 28 Clean Up Post Upgrade (as root user)
4.1 Rebuilding the RPM DB
4.2 Do Distro Sync
dnf distro-sync --setopt=deltarpm=0
4.3 Check All Your Config Files
Use rpmconf to find .rpmnew, .rpmsave and .rpmorig files. You can keep current version, place back old version, watch the diff or merge.
dnf install rpmconf rpmconf -a