Shall I upgrade Ubuntu 16.04 to 18.04 or manual installation through iso?

[inirobo]

I was wondering if I should make a clean Ubuntu 18.04 installation (using iso) or upgrade it in August or so through Ubuntu Update.

I have Ubuntu 16.04 LTS. I configured my PC to be notified when new LTS versions are available.

[Frogs Hair]

Hello and Welcome !

The safe upgrade via the update manager won't be available until the 18.04.1 release. I always prefer a clean installation and be aware that 18.04 uses the Gnome Shell rather than Unity, though a Unity session is available in the repository.

[Topsiho]

You don't need to upgrade 16.04 to 18.04 if you are still happy using it. It will be supported for some more years (until 2021).
But if you insist, best thig is, to my opinion, to do a clean install, when the first point release of 18.04 becomes available. In that I fully agree with Frogs Hair's advice.