Why is my iPhone so slow sometimes?

I got the iphone4 for graduation at the end of may 2012. And it's really slow sometimes. On my old phone I could call *228 and update it but i don't know if its different for an iPhone. I don't have that many apps I have a decent amount and my Internet connection is good. Is there somethin I can do to fix it?

I'll tell you this, DON't UPDATE YOUR IOS PAST THE MAIN FACTORY UPDATE NUMBER. For example if you bought that phone and it had ios 5.1 then you shouldn't have updated to ios 6.0 if so then sorry you can't do anything. To help though just keep your background apps closed when not using them and try not to play too many apps at once