How to Upgrade Python in Ubuntu
                     How To Upgrade 
Python in Ubuntu
Install ppa
Open terminal and run the following command to install the right PPA for python 3.6, 
3.7. 
$ sudo add-apt-repository ppa:deadsnakes/ppa
Update system packages
Run the following command to update system packages 
$ sudo apt-get update
Upgrade Python 2.x to 3.x
First we need to upgrade python to 3.6 and then python 3.7 
$ sudo apt-get install python3.6 
$ sudo apt-get install python3.7
Install pip
Install PIP for python 3.x 
$ sudo apt install python3-pip
Set Priority
Since we have multiple python versions on our system, we will assign priority for them. 
$ sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1 
$ sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.7 2
Thank You
Visit for details
https://techimbo.com/how-to-upgrade-python-in-ubuntu/