How should I upgrade python to 3.8.0?

[snippsat]

How can I upgrade python with pip?

You can not that's only for pip and modules/packages.

2) If it is not possible to upgrade python with pip, I don't want to keep several versions of python, how can I do this without loosing all my little programs that are inside my folder python37?

It's no problem to have several version i have had up to 7-8 and also Anaconda/PyPy..ect.

If you want to test out Python 3.8 just install,but can still keep 37 as main version in Windows Path.
Can access all version using py

# Main version in Path
C:\
λ python -V
Python 3.7.3

# Main version 
C:\
λ pip -V
pip 19.3.1 from c:\python37\lib\site-packages\pip (python 3.7)

# using py
C:\
λ py -3.8 -V
Python 3.8.0

C:\
λ py -2.7 -V
Python 2.7.9

C:\
λ py -3.4 -V
Python 3.4.2

# Example test out new walrus operator
C:\
λ py -3.8
Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:21:23) [MSC v.1916 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> lst = []
>>> while (current := input("Write something: ")) != "quit":
...     lst.append(current)
...
Write something: Python forum
Write something: hello
Write something: quit
>>> lst
['Python forum', 'hello']

So i talk about Environment Variables Path for main version.
If i copy out image from Python 3.6/3.7 and pip installation under Windows

If i had changed to Python 3.8 here,then it will be the main version.