To open the front cover off of the print head, first, place your index and thumb finger on the left and right side of the print head where the red circle indicates.
Second, squeeze the front cover and pull it off.
If you're having trouble getting the front cover to fit back on you can try this method.
First find the two black tabs at the top of the cover.
Next, using one of you're fingers try and lightly push up on the tabs. Don't use too much force or you could risk breaking the tab. You want to try and flex the tab back into a more straight position.
Lastly, Place the cover back into the extruder. If done correctly the tabs should grab and snap onto the first vent hole shown below