unable to change stats plugin API key

I signed up with www.ads-software.com and created a blog. Later I signed up with wordpress.com to use the stats plugin. However, I do not want my username appearing when I comment on other blogs and this is happening by default. I tried to follow the instructions to use another user’s API key for the stats plugin and failed. The instructions do not work. (other user = me with a 2nd account).

What I would like to do now is change my username on both .org and .com. I created such accounts already but haven’t succeeded in doing whatever is needed to switch, which I assume will involve clearing cookies and cache and making a change to my database.

Please advise and thanks in advance.