In addition to the comments from user36303 and JollyMort see this answer to my recent question about the difference between ring size and mixin. The distinction is clarified below:
Ring size = 'mixin' (number of foreign outputs) + 1 (your output)
I agree with the advice above that this task is not urgent and should be left to someone very familiar with the codebase. No find/replace script or other automated tool is appropriate here.