How to change apple id of iphone?

I'm currently using my dad's old iphone and i'm having problem upgrading apps such as whatsapp and Skype because it kept asking for the old apple id password.i've changed the apple id in the apple store and all. And I have no problem upgrading apps that i downloaded myself, but only for the apps my dad downloaded. Should I delete the apps and redownload it or something?

Factory reset the phone. And start fresh. Or you can make a new apple ID just for your self
all you need to do is go to your settings find iTunes & App Store then on the top it should say
" Apple ID: xxxxx@xxx.com" just click that. & it should give you 3 options
1: View Apple ID
2:Sign Out
3: iForgot
click sign-out.once you do that
click login and it should give you an option to login or make a new Apple ID;
click Make New Apple ID and make a new account.
from there you're able to start using you new Apple ID; & start downing apps