I once enlarged my basement window for the same reason. You can rent a tool called, I think, an "Impact Drill" and a masonry bit. The rental shop will know what you want. You just drill a series of holes to outline the new window shape and finish the job off with a hammer and cold chisel. It was pretty quick and painless in my case. It helped that my basement was unfinished and the window far enough above the ground to accomodate. I had a piece of plastic to throw over the sill so I could slide the boats in single handed.