Can i reset my iPhone 5 back to factory settings if I'm not selling it?

I used a lot of data and is it possible to reset it back to factory setting to save money? Is this a bad idea?

Added (1). If I reset it, will I still be able to use it or no?

Yes but you will have to take back to your provider to have re-activated again if you run a factory reset.

Listen if there's something in the phone that is not working well, turn off any application that is not needed in the daily use of the phone. Listen some applications run in the background using up gigabits while they are not in use, so do not let them run unless you are using them. Master the art of using the settings and application properties to control the operation of the phone. Also make sure you use the Wi-Fi and it is not also billing gigabits against your bill. Apple had a problem with that and make sure it is not happening on your phone. Lastly if you can use your home internet for a lot of things you might be doing with your phone, that can prevent some extra charges. You can go to the Apple store and the people there will help with the problems. Hey did you spend the 100.dollars to purchase apple care, it is a good investment to help you take care of problems for two years literally. It is cheap insurance to protect your investment which breaks down to 4.dollars a month. You have not had that phone long so you can still get it so give it some thought. Then when you go for help a year from now you can call or go to the store and get some. Secondly if the phone gets serious damage they will replace it twice under the warranty for a 100 dollar co-pay. That"s not bad for a phone that cost nearly 650 to 700 dollars. You probably do not need a reset just make adjustments in the operation of the phone.