Well, you'll need a spring compressor.
Remove wood stock - 2 screws on either side of the forestock and one screw forward of the trigger guard (not the one behind it like Gamo's are).
Put the receiver tube in the compressor and compress making sure the whole thing is secure in the compressor and that the presser foot clears safety. The FWB safety is situated in an awkward location and you have to offset the presser foot from that. You might also want to use a piece of leather or nonslip/non-marring material on the face of the presser foot because the FWB doesn't have anything that covers up the back end of the receiver tube.
Using a wrench, remove the "nut" (is flat of 2 sides and rounded on the other 2) that holds the trigger assembly together.
With the "nut" out, slowly back out the trigger assembly, making sure the safety blade doesn't come flying off because it's not held onto the trigger housing by anything (the safety is an arced blade and sits in a groove on top of the trigger housing following the same diameter). The trigger spring is right underneath the safety blade so if the safety blade pops off and the spring goes flying, you'll have to spent time looking for it.
Now with the trigger group in hand, remove the trigger blade taking special care to remove only the pins that hold the trigger blade in place. I recommend having the replacement trigger in hand before removing the broken trigger so you have an idea which pin(s) you need to remove to drop the trigger.
Install new trigger blade and reassemble the rifle in reverse order of disassembly. Make sure the trigger spring and blade are assembled correctly in the housing. What I did was wrap a rubber band tight around the safety blade and trigger housing, towards the back so the whole thing stayed together while reinstalling so you'd have two hands free. Otherwise, you'll have one hand holding the trigger group together while trying to press the spring, etc. When you get the trigger group inside the receiver tube enough that the safety blade won't pop off, remove the rubber band and finish pressing till the "nut" holes align and you can reinstall the "nut." Once this is done, you're good to go with putting the stock back on.
Good luck.