user names and user ids

I want to check which user in my neighbourhood didn’t accept the ODbL (via ito and the agreed user list) but ito only support user names and the list only supports user ids. How can I convert user ids into user name and vice versa? I can’t find via search or in the wiki (api, xapi, …).

OK, I got it, I have to go to the user page an have to look into a changeset. In the XML-view of the changeset (link on the bottom of the page) you can see the user name (user) and the user id (uid).