Geez people can be rude!
I would say that before you go completely changing your diet see if there are a few little things you can change. You said you have changed portion size already... do you eat too much full fat dairy? butter? chocolate? white bread? Sometimes just little changes can really reduce your kilojoule intake and it is easier to stick to it is it is fairly similar to what you eat already. That is what I think anyway.

Diet will make the biggest difference to fast weight loss, but do as much exercise as you can manage as the more muscle you build up the faster you burn energy, so it gets easier to keep weight off. I have always thought that fit looked better than just skinny too.

Good luck with it. Try to do it for yourself though... not for ignorant people who make rude comments.