How do I change the password in the icloud iphone 5 without the password of the previous owner?

You don't.

IF if previous owner did not turn off find my iPhone, you are out of luck.

REturn the phone to where you bought it or contact the previous owner.

Contact the previous owner and ask them to remove the device from their iCloud account. Once that is done you can erase and activate the iphone. There is no way you can do this without the assistance of the previous owner.