First, you need to have the latest stable version on your home P.C. in .zip format. tgz is also O.K.
Then, you need to use the File Manager in CPanel. From there navigate to:
/home/public_html/corsi
Upload the zipped file to this directory from your P.C.. Show File Contents
Extract File Contents
Delete File
Edit File
Change Permissions
Rename File
Copy File<
Move File
Extract File Contents
Delete File
Edit File
Change Permissions
Rename File
Copy File<
Move File
Click on Extract File Contents.
It should extract into the moodle directory that is there from the existing installation.
Close the File Manager and visit your moodle installation, log in as admin and navigate to the admin page. You should see a process for upgrading. When it is done, you should have the latest version installed.
Nothing else should have changed (courses, users, colors, etc.). However, you should read the list of changes that were made to Moodle to familiarize yourself with the new features, etc.