First, take the barreled action out of the stock and pull your bolt out. Next, take a look at the trigger mechanism. You'll see a flat head screw in the side of the trigger. Remove it. This will allow you to separate the trigger from the safety mechanism. Next, you'll see that the trigger pivots on a pin. Slide the pin out, making sure not to lose the spring at the rear of the trigger.
Once the screw and the pin are removed, the trigger should slide down and out. Now you can put the replacement in by just reversing the steps above.