question

You can edit, it is the very last option on the page. Go to Users > Select User > Meetings tab > Edit my meeting settings > Under the Meetings tab scroll all the way down the page to Invitation Email > Click the edit pencil. You should be able to edit there.

Are you also able to remove the "Hi There" portion? I'm not seeing that as an option. 

It is indeed a pencil icon, it creates a popup that you will need to scroll back up to see.  I cannot edit this template in any manner, it is locked.  You can type into the More Content area only.

The English on the site is a bit loose.  The Greeting "Hi there" is not desirable for me.  The phone number sets start out with "OR" and maybe that should be "For."  While I am a fan of Apple products, I would rather list the regular phone numbers first and the Apple numbers second because I live in a PC world for the most part and that Apple numbers only add confusion to my participants.

Basically, this thing needs to let us customize it with an HTML template and predefined XML tags or at least let us edit the blocks of text by making them editable.  

An easier way would be for us to be able to upload our own email template in Google or Office Outlook format.  

My two hacks to all of this are that I:
1.  Generated a default email from RingCentral to Outlook and then modified it to my needs.  I then selected File - SAVE from the Outlook screen and it sits in DRAFTS now.  I then use RingCentral to schedule the meeting and setup the times, but then open my DRAFT email and copy and paste the body of text that I desire. 

2.  You can also do this with Quick Parts in Outlook (Insert - Quick Parts or move the Quick Parts icon to the main toolbar in Outlook).  At least I get the text that I desire from a template hack.  A Quick Part is setup by drafting the email that you desire as a Template and then highlight all of that text.  Then select the drop-down in the corner of Quick Parts and pick the option at the bottom of that menu to "Save Selection to Quick Part Gallery..."
See:  https://www.webucator.com/how-to/how-create-quick-part-microsoft-outlook.cfm

Not perfect, but a time saver until they spend a few hours coding this.

Despite what their support pages might imply, you cant edit the template, you can only add content to it (very bottom of the template) . And yes, their template sucks. I too, would appreciate the opportunity to remove the unnecessary garbage, and rephrase it to fit my own vernacular.