Now the patch 1.03 for ArmA 2 is released offficially by BIS.
You can update from version 1.00 and 1.02 by just clicking the executive file after downloading.
Keep in mind that the update process can take some time to finish.
VERSION 1.03 HIGHLIGHTS
* Major AI tweaking and balancing (especially AI infantry can hear much less)
* Improved multiplayer and cooperative campaign (saving games, connection issues)
* Numerous fixes and improvements in the Harvest Red campaign
* New: Functions getPosATL and setPosATL to allow controlling position relative to terrain.
* New: command line option -showScriptErrors introduced to show errors in scripts on-screen
* New: Direct analogue throttle and brake for airplanes now available.
* New: More flexible configuration of Flares in the config (brightness, size)
* New: Mission name (with * indicated unsaved work) displayed in the mission editor
* New: Keyboard shortcuts in the mission editor
* Improved: better handling of gravitation for shots (esp. for grenades)
* Improved: Building destruction
* Improved: Better airplane HUD visibility both night and day
* Optimization: Reduced frame stutter near map borders.
* Hotfix: Players are forced to reconnect after MP Load on server.
* Fixed: no particles effect when hit object with destructNo
* Fixed: grenade could destroy a building just by impact
* Fixed: grenades may explode only on the final impact
* Fixed: when a grenade bounces on a ship deck, the proper particle effects is shown now
* Fixed: missiles should pass through vegetation
* Fixed: Player connected to loaded game was sometimes frozen.
* Fixed: Game crashed when launched on a system with more then 8 CPUs/cores.
* Fixed: Possible crash with laser designator active.
* Fixed: Sometimes crew of a close vehicle was visible through the vehicle.
* Fixed: Infinite looping of commands 'Stop' in radio.
* Fixed: Leaning 'limits' do not work in TrackIR.
* Fixed: Clients were often endlessly stuck in 'Receiving...' window after MP Load.
* Fixed: Rainbow could be visible even with sun below horizon.
* Fixed: 3D Editor - civilian and resistance units did not work correctly
* Fixed: Sea surface was not rendered in NE area out of map.
* Fixed: Terrain surface was sometimes using wrong parallax map.
* Fixed: Grenade could sometimes destroy a building just by impact
* Fixed: Radio messages sometimes echoed
* Fixed: Team switch did not work when player died
* Fixed: Reduced AI detecting slowly moving enemy vehicles by ear.
* Fixed: Prevent killed AI units reporting who killed them.
* Fixed: After respawn in MP, player's tasks, diary content and skills are transferred to the new entity
* Fixed: Leaning 'limits' did not work with TrackIR
* Fixed: MP client frozen in Receiving... screen sometimes
* Fixed: Problems with saving and loading games in cooperative campaign
* Fixes and improvements in most of the campaign missions (Into the Storm, Harvest Red, Bitter Chill, Manhattan, Badlands, Dogs of War)
* Improved: autosave logic to not save when it was not safe
* Improved: Eye for an Eye in Scenarios
* Fixed: Warfare fast travel on clients was not using logistic values
* Fixed: Warfare money sending
* Fixed: Warfare HQ multiple reports
* Fixed: First-Aid: Action module caused healing scripts to run twice
* Fixed: Supply drop not ending (wrong vehicle class)
* New: First-Aid modules work with respawn
* New: First-Aid ability to stop healing
* New: Added ability to add Support Requests that do not expire.
* Improved: First-Aid modules more robust and faster
* Improved: Better support for side Resistance in SOM / ACM.
* Fixed: Invisible driver in UAZ (MG and GL)
* Fixed: AI soldiers were able to hear extremely well
* Fixed: various minor problems on buildings
* Fixed: rocks destruction effect changed
* Fixed: penetrability of some vegetation
* Fixed: collision geometry of A_BuildingWIP
* Fixed: react FSM core conversations
* Fixed: cargo animations in LAV25
* Fixed: indicators in Ka52 when using NVG
* Fixed: cargo animations in BTR
* Fixed: Warfare keypoint on Chernarus
Read the original topic with the full changelog, install information and other here.