The bottom one is tough to get off, but basically I take the splash guard off from underneath the front bumper and then use a screwdriver to push the clips of the mesh, by poking through the front of the mesh. Then you just have to carefully extricate the mesh out of the bumper.
Once it's out, spray it down good with brake cleaner and let it dry. The apply a bumper primer, followed by the paint of your choice. Carefull though. don't mix paint brands as I have seen some of them react with one another and cause spot to appear all over the piece being painted.
If all else fails, by grills from me!