> I don't know technical details but i can successfully use this command: `pip install --upgrade pip`.

On Windows (and not under something like cygwin or msys, which have their own rules)? Anyway, it's not that important, the recommended approach is `python -m pip`, so whether using the non-recommended approach works or not doesn't really matter.

> On pip's issues tracker i was suggested to use `ensurepip --upgrade`.

Let's take that question back to the pip tracker. If you want the latest version of pip (as opposed to the bundled version) ensurepip isn't the right approach.