1. Login to Plesk Control Panel

2. Make sure that you have added the website under plesk. 

3. Click on ‘Files’ Menu on the left panel plesk 

4. Select ‘httpdocs’ folder

5. Click on the ‘Upload’ button on the top side options

6. It will prompt out a browse page and can select your Data (Multiple selections hold Ctrl button on keyboard) from your local system

7. Click on OPEN button and upload

8. You can also upload your contents using any FTP client software like ‘FileZilla’. To download filezilla refer here.