The next step is to flash the latest firmware using a program called Odin.For this you will need a PC. It is not without risk but if you follow the instructions properly you will be fine. You can download firmware from sammobile website. You need the latest firmware with btu csc. Its a 5 gig download. Using Google search for a tutorial for Odin which should give a link to Odin and a step by step guide.
Once you are done your phone should automatically update in the future. DON'T FORGET Back up your data before attempting anything.