Synology has released update number 3 for DiskStation Manager version 6.2.3-25426 for their own NAS systems. It has been showing up on your Synology since mid-December if you have automatic updates set.
If you always update your DiskStation manually, you can find the update in Control Panel > Update & Restore > DSM Update where you can then trigger it.
Presumably, this will be the last update for the DSM 6 version before Synology comes around the corner with number 7. The new version of DiskStation Manager is supposed to run on quite old devices as well – so you don’t have to worry that a two or three year old device won’t get the latest DSM version anymore.