1. If Filezilla is not installed in your computer so please install it first on your system from this site https://filezilla-project.org/download.php and you can also use another FTP client as you want like Filezilla i.e. CuteFTP, WinSCP etc.
2. I am considering FileZilla in this article.
3. Open FileZilla from your PC Programs or APPs, you can also search to write Filezilla into search bar.

4.  

5. In the top input fields you need to enter your website “Host address”, “Username”, “Password” and “Port #”, The port number is 21 for ftp connection, please have a look on below mentioned screenshot
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7. After successfully connected, you can see two sections for files or directory structure as mentioned below in screenshot. The left one is for your local PC directory structure and the Right one is for connected server directory structure.
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9. 9.On your remote site open public_html directory and paste all website content and files in this directory.
10. You can select your website location on your local system and right click on that file or folder to paste it on remote site directory as you want in public_html as mentioned in below screenshot.
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12. Your selected files or folder will be upload on remote site in selected directory.
13. 13.You can also upload compressed files like abc.zip etc.
14. But you need to extract that file after successfully uploading from cPanel.

How to upload your website from cPanel.

1. First open your cpanel link i.e. (www.yourwebsite.com/cpanel or www.yourwebsite.com:2083)
2. 2.If you open first time your cpanel url so it would required secure certificate save into your browser. Please note mentioned below steps to do this.
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4.        Click on Add Exceptions.
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6.  Click on this button.
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8.    Login Screen will appear as mentioned below.
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10.    Login into your cPanel with your credentials (username and password).
11. Click on this icon named with File Manager 
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13. 13.You need to open this directory named with “Public_html”. Double click on world map icon.
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15. Click on Upload icon.
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17.  You can select files from your local computer as mentioned in this below screenshot.
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19. Once you select the file from your personal computer and click ok to upload it will be on loading and mentioned you status with percentage %. 
20. After successfully uploading it will be convert to on Green color with 100%.
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22.  You can click on Go Back to “/home/yourweb/public_html”.
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24.     If you upload compressed file so you need to extract from related directory where you upload on server as mentioned in this screen.
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26. After click on Extract it will ask you about path by default it will show you the path where zip file exists, you can extract in your desired directory.
27. 

1. Open up your Plesk Control Panel.
2. On the Domains tab section click on [domainname.com] .
3. Click on the Websites & Domains tab.
4. Click on the File Manager Icon.
5. Click Root Directory in the menu.
6. Scroll over httpdocs and click the drop-down arrow
7. Select Change Permissions

   8. Once the Permissions page has loaded, check to make sure that any applicable users have full control on the files. 
   9. To do this select the user (ex. Plesk IIS WP User) and check the Full Control permissions box for the account in the right sidebar.

 
For further detail information you can read at this link https://docs.plesk.com/en-US/onyx/customer-guide/websites-and-domains/website-content/setting-file-and-directory-access-permissions.70738/