I build it from source on my own. This is in no way acceptable for consumers and it's beyond me, why it takes so long to offer the new version in the Ubuntu repositories.
After the installation with
sudo make install , you can remove the outdated version with sudo apt remove emacs24 emacs24-lucid emacs24-nox .That's necessary because the package emacs uses a strange version number (46.1) resulting to overwrite emacs 25.1 on any upgrade.
This is really an annoyance, but not the only one. The repositories need to offer new versions much, much faster.
