I personally think putting it in PATH is a better option rather than fixing it in vscode. This is because I work in tandem with vscode, vscode internal terminal, and a REPL running on an external terminal. It would suck to have vscode launch 1.6 (since the path is explicility specified) and version 1.x run when typing in julia in the terminal.
To answer your question directly, if you google “Environment Variable Windows”, you will get very explicit instructions. (For example: Setting global environment variables on Windows – Shotgun Support (shotgunsoftware.com). I would advise you to play around here and see what is inside the variable PATH.