How to set up an apple account on iphone?

I have my mums iphone 4s i got for my birthday and the apple account its connected to is hers. How do i set up my account (yes i already have an account) on the phone? Preferably using the itunes app or computer

Sign out of your mum's account, then sign in to yours on the phone itself. All your apps, music, games, etc should just drop to the phone if they are in the cloud.

If they are not in the cloud, then sign in to your iTunes account on your computer and connect your phone to the computer. You can then sync your apps, etc to the phone.

A final alternative is to perform a factory reset on the phone, via the settings menu, then set up the phone as your phone, with your sign in details. This will ensure a clean install, and ensure that your mum's stuff is completely cleared from the phone, leaving just your stuff on it.