It is great to hear that you are diving into creating an email that fits your needs! The best way to change the text that says "Alex --" or "Friend --" is to remove the Liquid variable "{{ recipient.first_name_or_friend }}". You can edit any piece of text within the body of the email blast. The WYSIWYG editor gives you the freedom to change exactly how the email looks!

Refer to the image below for the exact spot of the Liquid variable within the body of the email blast:

UPDATE: 
It is also worth noting that you can use a different "default" word besides "Friend" if you'd like. Rather than trying to edit the liquid variable that is already in there, you should just use the {{ recipient.first_name }} variable that is already in there and add a default filter, like so:

Dear {{ recipient.first_name | default: 'neighbor' }}