Woot! Good work SS, I knew they had to be somewhere.
Ok, so Taking the gun out, just reach up and rip that sucker out.
Then, you need to unclip the bumper, you might need to wiggle the side bits (that the wheels are connected to) a little to unhook the clasp bits, but once the bumper is free, the bonnet and windscreen area should freely move up.
Step 12 is the one where I find the rear wheels get in the way.
But generally Soundwave is pretty tough (it says so in his bio

) and can take a reasonable bit of force. But just be gentle and enjoy the experience. I always take my time when transforming a figure for the first time, it's a way to appreciate the engineering.