Uninstall python3.5

script.md

List all python versions in default locations

ls /usr/bin/python*
ls /usr/bin/ | grep python

To remove just python3 package

sudo apt-get remove python3.5

plus it's dependent packages

sudo apt-get remove --auto-remove python3.5

plus configuration and/or data files of python3

sudo apt-get purge python3.5

both configuration and/or data files of python3.5 and it's dependencies

sudo apt-get purge --auto-remove python3.5

How to install new version of python

sudo apt-get update

sudo apt-get install python3

Set python version for npm

npm config set python /usr/bin/python3.7

Also, see https://docs.python-guide.org/starting/install3/linux/