There are 3rd party tools that can be used to flash a new firmware for your phone but there is a possibility that the phone will brick resulting in being unusable anymore. The most simple and easy way is to access Software Update section from Menu > Settings > About device > Software update. In some cases you will be asked to create a username (that can be done from the same window). Make sure that you are connected to the Internet and have decent connection speed as packages will be large in size. This procedure is called OTA (Over The Air). If there is a new firmware update for your phone, you can proceed to install it. Also, the battery needs to be somewhere about 75 % of its capacity.