Like many people, when I got my initial certificate I used my social security number as my airman id. Only in the last few years has it really sunk in just how little one should use that for any purpose so when I got an email from my flying club today containing a link at which I could change it, I went straight there. My new certificate will be in the mail shortly with a shiny new identification number. If you want to do the same, and you probably should, try this link at the FAA website.