What is a political orientation that favors social progress by reform and changing laws rather than by revolution?

Generally speaking, that would be those of a Progressive bent (sometimes mis-labled Liberals). They seek change within the system. Those of a Conservative bent tend to want to preserve the existing system as is. Revolutionaries (or Radicals) generally seek to throw out the whole system and start fresh with a new one.

If you're on OdysseyWare, the answer is: liberalism