What is Upgrade SMR2 TO MR2?

The Alcatel phone received an AT&T Update message: "About this update - Upgrade from SMR2 to MR2 version." 

Okay, so what do those acronyms mean; is this a security upgrade, efficiency upgrade? 

And, why does the message begin with Update, then say it is an upgrade? 

For the end user to know whether this is important to proceed, there should be some explanation; including how long the installation will take. 

Any help is appreciated. 

bob