You mean 2.5.15?
You could register your gamespy cd-key with steam and steam will automatically download and update the game, if you dont want to use steam then you have to go to 1c ftp and download patches and install them manually.
http://www.1cfiles.com/MoWAS_patch/
if you have the game of the year version you get the big 2.5.13 goty patch and then small 2.5.15
if you have regular version then u get the regular version mow-as-update-setup-en-2.05.13-full.zip and then small 2.5.15