1. Extract the .zip file you downloaded from CodeCanyon.
  2. Upload and overwrite all the files same way you did when you first installed.
  3. Visit http://yoursite.com/secure/update url and click Update Now button.
  4. Once update is completed you will be redirected back to homepage.
No data will be lost on your site when applying updates.
Always use a desktop application like FileZilla to upload files to FTP as opposed to web based file managers to avoid issues with corrupted or not properly uploaded files.