How does one disconnect from a network share in Windows 7?

Delete all sessions net use * /del

Delete only one session net use \\servername\share /del

Show actual sessions net use

From users standpoint, it's easier to Map Network Drive from My Computer. Then it only takes right click and Disconnect.

When you just enter an UNC path as you describe, you're not connecting anything permanently, so there's nothing to "Disconnect" -- the server will drop the connection after it's been idle for a bit.

If you had mapped/mounted it as a drive letter, then you could "Disconnect" the mapping as you suggest, or how @week suggested in their answer. But you're not mapping it, you're just entering the (UNC) path for the one-time use.

Windows may be kind enough to remember the fact you used it, remember the related credentials, and offer it in dialogs and such, but it's just a remembered path, not a mounted connection.