Well, here's the deal. I'm not sure what command you need to use, but you need to specify the install directory. When you first tried the command it tries to write to the default linux directories for the server, which you don't have write access for. If you did, your install would effect everyone on the server.
So, you want to run the command to upgrade pear, but you need to specify an insatll directory of "/home/userName/pear" (chaning userName to be your username and pear to anything you want) Why don't you try asking over in the forum you linked to on how to specify the install directory.
You'll get it, just be patient. It takes a bit to learn, but once you begin to understand things, you'll be able to customize your sapce more and more.