Frist of all its good to write your question in Google.com you will see hundreds of sites showing how to update your android phone step by step in details. i would like to tell you there three methods to update your android phones firmware or software. 1: Through Samsung Kies. the official software which you install in computer and connect your phone to sync photos music ets and it also updates your phone. and its easy.
2: Update your phone through "Odine" software, you have to download your phones updated firmware from samsung official site. you can see more details in google.
3: If your phone has automatic update option in settings it can update itself.
I will catagories my recommendation by 3-1-2. try 3rd first thats most safe then 1st thats also safe and the 2nd method is risky but will go just fine if you follow its instructions. Best of Luck.