Confused with Apple ID

Hi,

We are new to Apple and purchased an iPhone5.

I set up my apple id last week on the iPhone, as well my icloud email. Well they were different so I thought why not change them to match up.

Online I changed my apple id to what I want, however, on my iPhone it still shows the old id which I no longer remember the password for.

So, my iPhone still shows the old apple id and wants that password for installing apps and what not........how do i get rid of this apple id on my iPhone to make a new one.

Thanks,