How to switch apple ID on iphone 4s?

I forgot my pin to my apple ID on my iphone few days ago, then I used my friend's apple id to turn my phone on and use it. Now I got my pin and want to switch back to my apple id, but I don't know how to do it.

Go into -Settings, iTunes Store. Sign out. Then back in with yours. You'll be all set.

-However, if you downloaded any apps from your friend's and you want to keep them without redownloading them (or purchasing again), and those apps try to update, then you'll need to put in your friend's password so that it will update.

-Really it's just a small inconvenience. Not a big one.

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