I already have an account on Stack Overflow, and have a guest account on Code Review.
I want to know if and how I can merge these two accounts. Any ideas?
I have heard that if credentials are the same between two accounts, the system may automatically merge them without human intervention. It was mentioned on the comments on this question, but I do not know the criteria behind that.
You can't do it, only a diamond mod can. You can go to the contact us link at the bottom of the page and submit a ticket explaining the circumstances.