move content from a folder with unknown name up one directory

I have data arranged as follows:

--parent_dir
   |
   --4Bz27go1c
      |
      -- foo.md
      -- bar.tar.gz
      -- baz.c
      ..

I have a parent directory with a known name and a child directory with an unknown name (represented here as 4Bz27go1c. How can I copy all the contents from inside the child directory and move it up to inside the parent directory and also delete the now empty child directory?

To be clear, the final result that I'm describing should look like this:

 --parent_dir
    |
    -- foo.md
    -- bar.tar.gz
    -- baz.c
    ..