On ubuntu you can add this PPA Repository and use it to install python 3.7:
https://launchpad.net/~jonathonf/+archive/ubuntu/python-3.7
Or a different PPA that provides several Python versions is Deadsnakes:
https://launchpad.net/~deadsnakes/+archive/ubuntu/ppa
See also here: https://askubuntu.com/questions/865554/how-do-i-install-python-3-6-using-apt-get (I know it says 3.6 in the url, but the deadsnakes ppa also contains 3.7 so you can use it for 3.7 just the same)
If you want "official" you'd have to install it from the sources from the site, get the code (which you already downloaded) and do this:
tar -xf Python-3.7.0.tar.xz
cd Python-3.7.0
./configure
make
sudo make install <-- sudo is required.
This might take a while