The Nokia 5800 got a firmware update just hours ago which adds Kinetic scrolling to the phone. The version V40.0.005 firware has been in development for quite some time and has been released finally.
You can update the firmware OTA ( Over the Air) or using Nokia Software Updater using a PC. OTA will be easier and you can do it just from the phone. Although the 5800 supports UDP or User Data Preservation taking a backup of your phone is highly recommended !
Do you see the update in your phone ? There is no change log available , so let us know what changes you see after the update .