Replace ROMAN NUMERALS

Hi everybody! I want to replace the text from a file that has some building heights in roman numeral format (II, III, -I+VIII...etc) indicating floors. I tried to use "replace text" but I happened to get some problems as when I try to change the number "II" for 2 the number "III" happens to become a 2 as it has those 2 characters also. There are a lot of varieties of numerals and the problem repeats with many other combinations, and I could go from longer and bigger strings to smaller ones but it´s a lot of work. I mean starting form the longest and bigger string and end with the smaller one.

I need to replace A for B but in the situation of AA not get BB but C.

:)