Warranty period starts from the date of purchase. For more info, please refer to Manufaturer's Limited Warranty page of your local Nokia site
You can update the software of your device using Nokia Suite or using the Software Update feature/function built in for the Asha 305 and these are the only methods recommended in updating the software of your device aside from going to a Nokia Care Point and have the authorized technicians do it for you. These are what you are referring to when you said manually, right?
The warranty will just continue as to answer your question!