My iPhone 3GS will not update?

My iPhone won't update and I've tried to update it from iTunes. What will happen is that it will say t was updated, but nothing really happened. I've also tried updating it from my phone but here are no updates and it won't let me download them. What do I do? What could be wrong?

Hi! Are you connected to the internet? It will only work if you are. Also the newest update needs atleast 50%. If nothing works take it to the apple store and ask for help. Service is free.