How I do:
# Remove python2
sudo apt purge -y python2.7-minimal
# You already have Python3 but
# don't care about the version
sudo ln -s /usr/bin/python3 /usr/bin/python
# Same for pip
sudo apt install -y python3-pip
sudo ln -s /usr/bin/pip3 /usr/bin/pip
# Confirm the new version of Python: 3
python --version