This post will show how you can easily upgrade ASDM (Cisco Adaptive Security Device Manager for ASA) to the latest version on a Cisco ASA5500 firewall using the command line interface. In order to do this you will need the latest asdm image (you will need a proper cisco cco user and contract to download this) from http://www.cisco.com/cgi-bin/tablebuild.pl/asa ; at this time the latest version available is 126.96.36.199 (asdm-61551.bin). You will also need a method to serve this file to the firewall, and normally this is done using a local tftp server (but you can also use an ftp, or even http server).
After you have the above things prepared, from the ASA cli (in exec mode) you have to run:
copy tftp flash
Address or name of remote host ? <- 192.168.1.1
Source filename ? <- asdm-61551.bin
Destination filename [asdm-61551.bin]? <- enter
This will download the asdm firmware on the firewall flash.
Now you just have to enable the new version, from configure mode:
asdm image disk0:/asdm-61551.bin
And finally you will have to reboot the ASA in order for the change to become active:
Note: replace the asdm filename with the one you are actually upgrading (might be a newer one for ex.) and also use the proper ip for your tftp server.