3/16 allen wrench
Phillips head screw driver
The plastic engine cover on the 335i is a bit more difficult to remove than some engine covers since 2 of the hex screws are under the cabin air filter cowl. You'll have to rotate the cowl forward once you get it free and that will allow you to get to the 2 hex screws.
I had a cracked engine cover so I wanted to replace it.
Loosen the two front hex screws with the 3/16" allen wrench.
You'll need to remove the five small bolts with the 5/16" socket indicated by the small blue circles. Also there are some plastic covers on each side, marked by a red "x". The plastic covers are removable just unclip the plastic tabs.
Next to each plastic cover is small bolt you'll need to unscrew from each side using the 5/16" socket.
Looking at the engine bay from the front of the car you'll see small electric clip on the left side next to the cabin air filter. Gently twist the clip and rest the piece to the side out of your way.
You'll now need to carefully unsnap three tabs in front of the cowl indicated by the blue circles in the image below. Be gentle, they are easy to remove and don't require much pressure.
Now you can loosen the cowl and rotate it forward to expose the back of the engine cover. There are two hex screws you'll need to loosen and if you have a magnetic socket, I highly recommend it so you don't loose the bolts in the engine bay. Loosen the two front bolts and now you can remove the engine cover and put on the new one or do whatever else you needed to get to.
Resemble everything in reverse order and you should be all set.