Close, pull off the three pronged plug gently,there is a rubber grommet behind the bulb you need to pull off. Then there is a bent wire holding in the h4 bulb, you need to unhook it and swing it away, remove the bulb. It has three locating tabs and when refitting have a look as to where the new one goes.
Then just reverse the steps to re assemble.
Take out the battery and have a good look, it'll make sense