If you decide to update to HMC release 7.3.5, Fix Central only supplies you with ISO images.
The sual update procedure requires to be physicall located at the console and update from the DVDs.

This procedure describes how you can update your HMC using the network without having to sit physically in front of the console.

1. Perform the "Save upgrade data" task using either the Web inteface or the command line.

2. Get the required files from the IBM server using ftp protocol using the following command:
  
   getupgfiles -h ftp.software.ibm.com -u anonymous --passwd ftp\  
   -d /software/server/hmc/network/v7350

Hint:
Once this procedure gets interrupted for any reason, you need to reboot our HMC before restarting it.
Otherwise, some files will remain in the local download directory which will lead to incorrect checksums.

You can check the progress of the procedure using the command ls -l /hmcdump in a different  terminal.

Once it has finished, you will see a prompt without any addtional messages and the directory will be empty.   (Files will be copied to a different location).

3. Tell the HMC to boot from an alternate media by issuing the following command:

   chhmc -c altdiskboot -s enable --mode upgrade

4. Finally reboot your HMC with the following command from the console:

   hmcshutdown -r -t now

The installation should start automatically with the reboot. Once it has finished you should be able to login from remote again. The whole procedure takes up to one hour.

Once you have finished you should add in any case the mandatory efixes for HMC 7.3.5.