I was stuck with my first linux MacBook Pro (17" 2007 core2 duo era) with no possibilities to either read an USB other than MacOS and it didn't recognize my CD-RW for installing something else, so I wondered if it was possible after all to update from Loki 0.4.1 to Hera 5.1.
I can assure you that it is possible and that the result is great! Hera uses seemlessly (I didn't check) less ressources, runs smoother, and close lid suspend/resume is now working fine and fully supported.
Now please backup everything first, and take my word of caution: I did encounter a small error but it could be solved along the way, but you have to be ready to work it out in console-only mode. I really advise to do so to avoid upgrade issues.
I recommend to follow this post's green V'd reply
Nevertheless, I followed a simpler route than in the above post reply: I only backed up the indicated files in the post, but I didn't remove them, and I only did that and the update worked fine.
Look in advance for the way to log off graphical mode on Loki: This worked for me:
session=`loginctl session-status | head -n 1 | awk '{print $1}'`
loginctl terminate-session $session
The error that I encountered is as follows:
libdvd-pkg: 'apt-get check' failed
to which I did only the following (which was then fixed by simply resuming the update process):
sudo apt remove libdvd-pkg
I had to reboot and install from console again, as in recovery mode (push escape on reboot to reach grub), and from the login screen (Fn+Ctrl+Alt+F1) to go to login, login and password then restart the apt instructions again to continue the upgrade. My screen blacked out repetively due to the login mode timeout, but I could see by (Fn+Crtl+Alt+F1) again as many times as needed. It's a little adventurous for the less experienced but it worked!
Don't forget to clean everything as the post indicates, by
sudo apt autoremove
Once the whole upgrade procedure is done.
The update goes straight from Loki to Hera.
Enjoy!