KB ID 0000704 Dtd 02/11/12
Your ASA will (by default) update your AnyConnect clients to the latest client software when they connect. However you need to supply the ASA with the updated packages first.
1. Download the latest AnyConnect client package, from Cisco. The one you want will have a file extension of .pkg
2. Connect to the ASDM > Configuration > Network (Client) access > AnyConnect Client Software > Add.
4. The file should upload to flash memory.
5. And it will tell you if it has been successful.
6. Select the new software and, using the ‘up arrow’ move it to the top of the list > Apply.
Note: At this point I also delete the old software packages.
7. Remember to save the changes. File > Save running configuration to flash.