Installed:

$ hmc version -i hmc01
hmc01 V9R2 SP950
$ 

Update to the recommended service pack:

$ hmc flrt -l hmc01
HMC and vHMC

Current
HMC V9 R2 M950
Released: 2020.11.20 EoSPS: 2021.04.23
Download: http://www.ibm.com/support/fixcentral/quickorder?fixids=MH01870&function=fixId&includeRequisites=1&product=ibm/hmc/9100HMCppc&source=flrt
...
Recommended Update
HMC V9 R2 M953
Released: 2022.08.18 EoSPS: 2023.04.30
Download: http://www.ibm.com/support/fixcentral/quickorder?fixids=MH01934&function=fixId&includeRequisites=1&product=ibm/hmc/9100HMCppc&source=flrt

Available Fixes
MH01944 
Released: 2022.11.17
Download: http://www.ibm.com/support/fixcentral/quickorder?product=ibm/hmc/9100HMCppc&fixids=MH01944&source=flrt
MH01959 
Released: 2023.05.26
Download: http://www.ibm.com/support/fixcentral/quickorder?product=ibm/hmc/9100HMCppc&fixids=MH01959&source=flrt
...$ 

Backup:

$ hmc bkconsdata hmc01
INFO: using ftp://fwtrans:abc1234@172.30.57.57//export/hmc/hmc01Generating the list of files to archive....
Creating archive file....
Offloading archive file....
Shared connection to virt-hmc-s01 closed.
$ 

Performing the update:

The SP HMC_Update_V9R2M953_ppc.iso was downloaded and placed on the NIM server.

CorrectiveServiceLocation has the following value:

CorrectiveServiceLocation ftp://fwtrans:abc1234@172.30.57.57//export/hmc

The update can then be easily started using “hmc updhmc”:

$ hmc updhmc -r hmc01 HMC_Update_V9R2M953_ppc.iso
INFO: using ftp://fwtrans:abc1234@172.30.57.57//export/hmc/HMC_Update_V9R2M953_ppc.iso
Corrective service file offload from remote server in progress...
The corrective service file offload was successful. Continuing with HMC service installation...
Verifying Certificate Information
Authenticating Install Packages
Installing Packages...

Broadcast message from root@hmc01 (somewhere) (Mon Nov 27 15:21:07 2023)

The system is shutting down for reboot now. 

Shared connection to hmc01 closed.
$ 

Since the “-r” (reboot) option was used, the HMC will automatically reboot after the service pack is installed.

After the reboot the new version is active:

$ hmc version -i hmc01
hmc01 V9R2 SP953
MH01934 - HMC V9R2 M953
$