How to: Set User Connections (SQL Server Management Studio)
Use the user connections option to specify the maximum number of simultaneous user connections allowed on SQL Server. The default is zero, which means that unlimited user connections are allowed. You must restart SQL Server before the change will take effect. Execute sp_configure to view the currently running value.
In Object Explorer, right-click a server and click Properties.
Click the Connections node.
Under Connections, in the Max number of concurrent connections box, type or select a value from 0 through 32767 to set the maximum number of users that are allowed to connect simultaneously to the instance of SQL Server.
Restart SQL Server.