Put your own bin directory in front, then see both copies

Answer

echo $PATH mkdir -p ~/bin PATH=HOME/bin:PATH export PATH type -a python3

type -a lists every hit in search order, so you can see your copy shadowing the system one rather than guessing. The change lives in this shell only.

Sarwar & Koretsky 3e ch2 §2.6, §2.8.4; ch7 §7.4