SQL Server having a performance problem... what can i do?

It is a basic method.
Before the Action, you must have a deep consideration about this query.
Because killing process, although it is simply select query, someone experience the problem.
But if you have only a little experience of SQL server, it would be a possible choice you can.

Open the Microsoft SQL Server Management Studio

Open the Activity Monitor

You can find qry of having a lot of CPU and Memory.
 

To check the qry, double click the process.

If you want to kill the process, click the mouse right button.
and then click the kill process.