In order to install your DNN into your httpdocs folder please follow these steps:
1. Remove any current DNN installations.
2. Install your DNN from your Web Applications in Plesk.
After the installation is finished - DO NOT OPEN the application in your browser.
3. Move all files from your DNN installation folder to your httpdocs folder via FTP or Plesk File Manager.
4. Fix the folder permissions from your Plesk control panel.
5. Open your domain name in your browser and finish your DNN installation.