You can get the latest OS 3.54 or 3.87 as an upgreade through Sweetwater or mostly any local music retail outlet. You need to have it installed by an authorized service center.
It is a piece of hardware that must be installed in your K2000. Unless you really know what youre doing I would suggest you have the service center do it. You could corrupt the whole system if not done properly.
Also,I think there is a download section in Kurzweils main sight where you can get a free download of 3.54 to disk, but you have to load it everytime you turn on your synth and I dont think it gives you all of the disk upgrades as the hardware upgrade does.
For more detailed info, contact Mike Martin in the K2500 zone or in SoniK.
sonikmatter.com