Uh, no they absolutely are not soldered in. Please don't comment if you don't really know. I just took out my cpu yesterday, in an hp pavilion dv7.
I would not recommend upgrading to the i7, the case isn't really designed to cool it well enough.
What if you were to upgrade the fan to a fan with higher output?
that would cause world wide power outages, mass chaos, and the panic would cause the flu virus to mutate into a new strain causing a zombie apocalypse. All because you want a bigger processor! Just leave it alone or buy a newer computer.