The blog post and the press release from Logitech don’t actually say the update is available now; they say it should be available soon.
The firmware version which incorporates this functionality has not been publicly released by Logitech yet.
Note that, for situations where you want SmartThings to control the Logitech Harmony (rather than the reverse), we will also need SmartThings to finalise the testing of and then release their new cloud-to-cloud integration which @thegibertchan posted about here.