source:http://support.citrix.com/article/CTX127455

To update an HA netscaler, do the following steps.

Upgrade the secondary netscaler appliance

1. Save the config: save config
2. Switch to shell: shell
3. Change to the installation directory: cd /var/nsinstall
4. Create a temporary directory: mkdir x.xnsinstall
5. Chang to the created directory: cd x.xnsinstall
6. Upload the files to the temporary directory (e.g. pscp build-11.0-66.11_nc.tgz nsroot@192.168.1.1:/var/nsinstall/11.0nsinstall/build-11.0-66.11_nc.tgz)
7. Extract the files: tar -zxvf ns-x.0-xx.x-doc.tgz
8. Install the software: # ./installns
9. Press y to restart the appliance
10. Check the state of the appliance: > show ha node
    This should state that it is the secondary node and synchronization is disabled. To disable the synchronization manually run the command: > set node -hasync disable
11. Check the configuration
    The version can be found with the command:  > show version
12. Failover the appliance: > force failover

Upgrade the primary netscaler appliance

1. Follow step 1 to 9 mentioned in the previous section
2. Check if the appliance is UP and it is the primary node: > show ha node
   If the appliance isn’t the primary application a failover can be initiated: > force failover

Enable Synchronization

1. Log on the secondary node, check if it is the secondary node: > show node
2. Enable synchronization: > set node -hasync enable
3. Check synchronization status: > show ns runningconfig

The update has been completed. Additional backups can be removed as well the downloaded files in the created directory (step 4).