If I change my engine from a 350 to small block 400 500hp 473 ft lb torque would I have to change the computer as far I see the carburetor is controlled by the computer

 

Depends on the cam.

The amount of "control" that the "computer" has over it, is rather minimal. There's enough mechanical adjustment in it to make it work. That's not really the issue though; the problem is that the idle passages are too small to fuel a large motor comfortably if the vacuum is too low. Speaking strictly as someone who had a 400 in my car for a long time.