Uninstall or delete modules when upgrading 6 to 7?
Updated after re-reading your question. :)

The process for completely removing a module is generally:


Backup your site.  The Backup and Migrate module is great
here too. 
Disable the module. Admin -> Modules -> Uncheck module ->
save. 
Uninstall the module - Goto yoursite.tld/admin/modules/uninstall ->
Check Modules to uninstall -> Click Uninstall
Delete the module - Delete module directory.




Additionally you can find details regarding upgrading from previous versions of Drupal at drupal.org.

Another useful module is the Upgrade Status module.  Listed only for reference.