There isn't an official way to upgrade Android on your phone to 4.1.2 JellyBean because Samsung chose not to release it for this type of phones. Latest version is 2.3.6 but if you want to take on the challenge, you could always try ROM for your phone, you can get on XDA Community. Make sure you read all the instructions for every ROM. However, I must warn you that you can end up bricking your phone and the ROM you'll be installing will have bugs/errors.
