To upload a file through cPanel file manager, do the following:
Log in to cPanel.
Under Files, click File Manager.
Choose Web Root and Show Hidden Files, then click Go.
Click to open the folder you want to upload files to.
Click on Upload from the upper toolbar.
Click on Browse (some web browsers might have Select File instead).
Select the file on your computer that you want to upload.
Once the file is selected, it will automatically upload. You can select additional files while uploading is in progress.