there are lots of good videos (youtube etc) showing the techniques involved.
It looks easy on the videos, but I've never done it, so I cant say for sure. Its probably a lot harder than it looks.
Personally, unless the front windows are also tinted to match the rears (which is of course illegal) then I think a half-tinted car looks odd and unbalanced. I would leave it alone, but its all a matter of taste of course.