1. Use DisplayPort connection.
2. Set monitor to freesync mode (this will be monitor specific, not sure if your monitor has a setting or not)
3. Crimson settings->Display tab->Fressync on or off toggle
In my experience if you do #1 and #2, Crimson drivers automatically enable freesync.
Edited to remove erroneous information.
Not true Freesync can work over HDMI too but the monitor has to explicitly support that and that one doesn't since Freesync only works on Displayport with that monitor.
The Catalyst Control centre is now replaced by Radeon Settings and the Freesync controls are in the displays tab. You will need to enable Displayport 1.2 see page 30 of the manual.
The manual for that monitor mentioned that he must use a DP connection.
Thanks for letting me know about the HDMI support. If you want to hear something funny, I recently bought a new monitor that supports freesync of hdmi, I just thought it was a typo or an error.
Thank you all! Turns out I didn't actually get the latest drivers (even though the auto updating software from AMD said so). Anyway, sorry for wasting your time...