Can't get rid of old version of python

[Ciarán Ó Duibhín]

Many thanks for both replies.  Everything seems fine now.

Reinstalling the packages using "py" made them available in v3.9.6.  So 
I could delete them from 
C:\Users\...\AppData\Local\Packages\PythonSoftwareFoundationPython.3.8.qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages
In fact I deleted the whole of 
C:\Users\...\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8.qbz5n2kfra8p0

Asking where "python" finds its (supposed uninstalled) v3.8.10 
executable was sending me to
'C:\Users\…\AppData\Local\Microsoft\WindowsApps\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\python.exe'
but deleting as above meant there is no longer a "python" command to 
worry about.
I may try to remove that whole subdirectory of WindowsApps and the 
somewhat similar one in C:\Program Files\WindowsApps

I think any other applications that use python probably have their own 
copy of python.exe — LibreOffice and GIMP 2 certainly have, with version 
numbers which are different again.