Never change for anyone, come what may. All of us are unique and should maintain our individuality. People and circumstances might force you to change but you should not yield and maintain your true character in every situation. Try evolving into a better being and adding on to your merits and good qualities. But don't get offended when people say that you are outspoken in case you are a loquacious person. If you enjoy talking blatantly and love to be vocal about your views, that's perfectly alright. You don't need to mend your ways.
Similarly, people might find fault with your physical make-up and might advise you to shed weight or gain some. The best thing about advice is that you can take it if you feel it's correct and will do you good. Advice that is given to you to make you feel low deliberately should be listened and then disregarded if you feel that the advice will do you no good. You are the best judge of when to change and when not to change.