Q: My wife old iPhone died and she is now using my sons old iPhone 5s how do I remove his contacts and text messages and add her contacts?

The following has instructions on how to clear an iPhone that is being sold or given away to another person: What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

Then, if she had a backup of her old phone on iTunes or iCloud, the following has instructions on how to transfer that to her new phone: Transfer content from an iPhone, iPad, or iPod touch to a new device - Apple Support

If she had her Contacts synced to iCloud they will automatically transfer to the new phone if she goes to Settings > iCloud and turns Contacts on after she has signed the new phone into her iCloud Apple ID.