Is it necessary to make drastic dietary changes for ibs?

Depends: If you have constipation as major symptom you may be better off with lot of fibre containing foods. If you have diarrhea as the symptoms, you may have modify your food to reduce the diarrhea.

Several: Regular consistent meal times and quantities of food, plenty of fluids and a good high fiber diet. You are retraining your bowel. Avoid caffeine and alcohol. Whether these are drastic or not is very subjective depending on what your diet currently is. But mot patients with ibs have horrible eating and drinking habits. If this is you then answer is yes if you want to feel better.