I'm using steam and struggled a bit with the patch to 1.6.01. Couldn't make sense of the 6 updater fast enough so I decided to try it manually. In the end, this is how I ended up doing it, with no problems.
Exit steam, close ArmA II.
open windows explorer to C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\@DayZ\addons
compare the version numbers of the rar files offered from http://www.armafiles.info/dayz/
(choose a mirror) for update against any previous updates you've applied, especially dayz_vx.x.x.rar, dayz_code_vx.x.x.rar dayz_weapons_vx.x.x.rar, dayz_equip.rar_vx.x.x and dayz_vehicles_vx.x.x.rar
download any updated files. (if you're not sure, get them all, see next 3 steps)
move the downloaded patch files, unextracted, into the @dayz folder.
extract the new files using extract here, overwriting the old files.
delete any old versions of the rar files you've updated (good houskeeping, you'll always know what version you're patched up to, rar files have version numbers, .pbo files don't.)
Restart steam and launch Arma II CO.
As I said, I patched my Steam version up to 22.214.171.124 days ago this way and have had no problems. Personally, I'm going to skip any patches not offered at www.armafiles.info/dayz
. this one isn't up there yet, so I'll hold off.