Sounds like you're experiencing many of the same issues we did upon the purchase of our new and first smart phone. Ideally, you will have to do some homework as to rule out what apps are constantly updating or simply running in the back ground. This can be accessed via the apps manager within your settings options.
Eliminating those unwanted apps which come from the manufacture loaded with tons.. will help reduce the slow nature of the smart phone. If you're unsure what apps to turn off or leave on.. Opera max can help you adjust and save data & memory usage during peak hours of the day. leaving your smart phone one all night without adjusting these app, can and will drain data etc for the first couple of weeks.
But if' you're not into the Opera Max thing.. you can use your app manager to systematically disable all apps within the manager.. which is very time consuming. Un-checking check etc.. It's best said, that one should not be afraid to explore their smart phone or even do a factory reset just in case you make a mistake.