sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt update
sudo apt install python3.9
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.8 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.9 2
python3 --version
sudo apt remove --purge python3-apt
sudo apt autoclean
sudo apt install python3-apt
sudo apt install python3.9-distutils
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
sudo python3.9 get-pip.py

these commands helped me upgrade python to python3.9 and installed pip for the python3.9 version.