Disconnect the negative battery cable. This is a safety precaution.
Switch off the fuel pump. Take your wrench and disconnect the fuel line from the fuel rail (over the engine). Plug it.
Connect the tube of your fuel injector cleaning kit to the fuel rail.
Start the engine. Let the solvent from the fuel injector cleaning kit run through the engine. This will take a few minutes. When it runs out, the engine will shut off.
Switch the fuel pump back on and reconnect the fuel line. Tighten it down with your wrench; a leaking fuel line can be very dangerous.
Start the engine again. Listen for any irregularities. If it still sounds like there is a problem, repeat the process or take your car to a mechanic.