Expanding a window downwards in a brick face
Removing bricks is easy.  It's putting them back up, properly, that takes some skill &amp; experience to do right.  It's been my experience that anytime you have someone do brickwork for you it gets expensive.
But in your case, if it were me, I would use a circular saw with a concrete cutting blade on it and just cut the bricks below the window vertically along the edge of the new opening, like this:

Then just chisel out/break the bricks off along mortar joint and remove as many rows pf bricks as needed.
Frame in for the new window with appropriate attention to weather proofing.  It looks like that might be a load bearing wall, so there's probably a header above that window that needs to be handled properly.  This post was mainly addressing the brick removal question.  There are a fair number of videos out there that walk you through the details of replacing a window.