Q: how do i switch accounts on my iPhone

1. Create  Apple ID's for your parents.

2. Delete the your iCloud account on their phone

3. Sign them into iCloud with their new ID's

Note that for the iTunes and App store account, this is a separate procedure.  They won't be able to update apps or play music/media purchased under your account.

Apple IDs and iCloud

iOS: Changing the signed-in iTunes Store Apple ID account