[support] Updating Themes and modules in Drupal 7x

When I try Drupal 7 to update a theme of module it wants the username and password of my FTP. Why? Lately if I use drush up for modules Drupal 7 breaks and has to be reinstalled.

How do I tell it the FTP of my home pc when I am using home pc?

What FTP details does it need to update themes and modules on a remote server? Mine or the secure ones for the server of some login detail for Drupal.org I see no reason to use username and passwords when it clearly states that it is a breach of security?

Anyway, is the any way to securely use the update process in Drupal 7? I haven't found a tutorial that discusses this in detail and gives precise methods to use the update tool.

Can someone help please thanks Roger