If you want to update a contact’s phone number, you'll need to Archive the current contact first, then add a new contact using the updated phone number.
Phone numbers are unique identifiers in Text Request, and cannot be changed.
You can only choose to delete an incorrect number if it has no message history.
To Archive a number:
1. Select the number from anywhere in your menu
2. Switch the contact to the Archived option in the new window that opens