This just seems nonsensical to me. Apparently, you cannot change user passwords via CLI in vShield Manager 5.1.2, but you have to go through the rigmarole of removing and recreating accounts. Specifically, I needed to change password for admin account.

Moreover, CLI admin account is separate entity from admin account used in conjunction with web interface!

So, first create a temporary admin account and log out:

manager# config t
manager(config)# user tempadmin password plaintext pass1
manager(config)# exit
manager# write mem
Building Configuration...
Configuration saved.
[OK]
manager# exit

Then log back in using tempadmin account, delete admin account and re-create it using desired password:

manager# config t
manager(config)# no user admin
manager(config)# user admin password plaintext pass2
manager(config)# exit
manager# write mem
Building Configuration...
Configuration saved.
[OK]
manager#

…and finally, logout as tempadmin, log back in as admin and remove tempadmin account:

manager# config t
manager(config)# no user tempadmin
manager(config)# exit
manager# write mem
Building Configuration...
Configuration saved.
[OK]
manager#

More on this is here… And yes, article recommends removing admin completely.