You may edit another users' information if you have User-Wide priviledges. You may always edit your own user info.
You may edit general information such as username, email address, phone number, address, etc. If you have system-wide privileges, you can grant or revoke the same system-wide privileges for a user. For example, if you have SC-Wide and User-Wide privileges, you can grant or revoke User- and SC-Wide privileges from another user on this page.