There is a large magnolia tree in our front yard, already a mature tree when we moved in ten years ago. The problem is that it has become so large that it is beginning to interfere with our sidewalk, our garage roof, and we are unsure of the timing or extent of trimming without killing the tree. It is beautiful and we are amateurs. We live in NW Indiana. Sould we rely on professionals and not trim it ourselves. Please advise us if you are knowledgeable.