The best method of finding user information is to click the user's name in SharePoint.
For example when you add a new user to your site collection, click the user's name and a page will open with user details. On this page will be the Account which includes the authentication identifier (e.g. "i:0#.w|") and the "SAM" (e.g. MG2\user_domain).
In SharePoint Foundation user information can be edited directly from this page by clicking on Edit Item:
In SharePoint Enterprise, follow these steps:
- Go to your admin URL (SharePoint URL/Admin)
- Click on Manage User Profile Application
- Click on Manage User Profiles
- Search for the user
- On the users item’s drop-down menu, select Edit My Profile
- Update the fields as needed
- Save and close the profile (all the way at the bottom of the page on the right)