How do I control (increase) lighting in Edit Mode? Some parts of my object are really dark, making it hard to edit.
You can control the lighting of the mesh via the user preferences. However if some of the faces are dark and others not, it is a telltale sign of a certain flaw in your mesh: normals pointing inwards. You can fix it by selecting all (A), hitting space and looking for Recalculate Normals.
If you want to read up on normals, see Wikipedia: https://en.m.wikipedia.org/wiki/Normal_(geometry)