First, you need to log in to your Plesk panel.
You have a username, and the password. You can also reset your password using the username and email. If you have any issues with that, just contact us.
Click in Files:
You will see all the files on your website and it works just as the files on your computer.
You can copy, or move them.
Clicking in MORE you can check its size or change permissions, and clicking on the 3 bars on the right side in each row, you can also rename that file.
You can also click on ADD to upload files from your computer.
Clicking on the name of any folder, you go inside the folder, and clicking on a .php, .html or editable file, you can edit the file and save it, and it will be easily synched to your website, applying the changes in seconds.
If anything didn't go right after changes, just follow the same steps to undo the changes!