Run the "Performance Restoration Software" package.
This will apply the new updated firmware, then do a full read/write to the SSD to eliminate any potential slow-downs caused by an issue you may have read about. The new updated firmware prevents this issue from happening in the future.
I'm not sure why they didn't put the new firmware into Samsung Magician but likely it's because very few people actually have slower SSD's due to this issue so they would rather not force it since any firmware update poses a small risk of data loss.
They will probably put the new firmware into Samsung Magician once they evaluate how reliable this firmware is for early adopters.
*I ran this on my 1TB Samsung EVO using the Windows version (not DOS) and...