How to make VSCode to replace the word when accepting autocomplete hint?

You can set this using the "editor.suggest.insertMode" setting. If you set this to "replace", it will behave as you want.

This feature is not yet implemented. A feature request has been opened on VSCode GitHub page[1]. At this moment there are no further details about when it could be implemented.

[1] https://github.com/Microsoft/vscode/issues/10266