I used the command below to upgrade to python3.7

But when I control the python version, it is still python 2.7.
How should I do?

I used the command below to upgrade to python3.7

But when I control the python version, it is still python 2.7.
How should I do?

Have a look at the instructions provided in this answer:
Then you would just call Python like so:
python3.7 ./yourScript.py
Do not forget to use python3.7 instead of python.