Go to Settings > Messages, where you can:

  • Turn iMessage on or off

  • Notify others when you’ve read their messages

  • Specify phone numbers, Apple IDs, and email addresses to use with Messages

  • Set SMS and MMS options

  • Show the Subject field

  • Block unwanted messages

  • Set how long to keep messages

  • Filter unknown senders

  • Manage the expiration of audio messages and video messages created within Messages (audio or video attachments created outside of Messages are kept until you delete them manually)

Manage notifications for messages. 

Set the alert sound for incoming text messages.