go to https://id.arduino.cc
another way to reach it is clicking "profile" on the menu bar, but only when you are on "Reference", "Blog" or "Playground", if you are on "Forum" the forum profile is opened instead because the default bar is replaced by forum commands.
(I know that this arrangement seems "strange" right now, but it's the basement to have multiple services (that we are implementing) around a single account.