You can read the information on Meta Stack Overflow under "[How do I change my OpenID][1]":

> This is documented on the [Stack
> Overflow
> blog](http://blog.stackoverflow.com/2009/01/we-now-support-multiple-openids/).
> 
> Go to your user page and click **add
> openid** or **change openid**.
> 
> <img src="http://blog.stackoverflow.com/wp-content/uploads/openid-multiple-association-2-new.png">
> 
> Note that once both are populated, the
> **primary** OpenId will be overwritten if you associate another OpenID.
> 
> You can use the [swap] link (not
> pictured) to switch your primary and
> secondary OpenID at will.
> 
> After changing, beware that copying
> your profile to other accounts [does
> not copy the OpenID
> details](http://meta.stackoverflow.com/questions/5656/copy-profile-from-stack-overflow-didnt-copy-alternate-openid/6018#6018).


  [1]: http://meta.stackoverflow.com/questions/793/how-do-i-change-my-openid-providers