You can use update. Here's an example of the process - http://communities.vmware.com/people/vmroyale/blog/2011/09/15/updating-esxi-5--single-use-esxcli-how-to. In the example you'll see that the --server option is used because the command is run from the vCLI (which is preferred over doing it on the host).
You only have to install the lastest patch as they are cummulative.