I have built a custom component in joomla 2.5 and want to know how to issue updates either in the form on an upload package installed via the joomla 2.5 installer or a trigger in main component upload package if already installed to upgrade to the new version im uploading. I assume i will also need to create version numbers in my component. Obviously if upgrading i only want the files i want to change replacing.
You have 2 choices. You can either use the Joomla Update Manager method, or use Akeeba Release System. Personally, I would use the Akeeba extension as it's much more flexible and contain many more features. For new versions, you will need to zip up the full extension, not just the files you have edited.