I see two options here: firstly changing for yourself and secondly changing for another person. In both cases, what is necessary is wanting to change. If you don't want to do it, nothing else really matters.
It all comes down to reflection though, that internal little thingy. By stepping back and looking at what you what to change, you'll have to make a note to always stop yourself before you do / say whatever it is you want to cut down on or change completely. At first that will be a change solely on how you act, but the more time will pass and the more you hold the reigns on yourself tight, the more subconscious it's going to become, thus, in the end leaving you 'changed' after a lot of effing effort.
Nevertheless, i've gotten tired of people telling me that i should "<insert a synonym for 'change'> for myself and nobody else". In my own brain that's bollocks. I'm sure there's some of us who will want to change for other people, and the fact that they want this X part of us to change actually makes us want the change too. Or, even if there's times when that change seems horrific and impossible to achieve, you still know that at least "that other person's helping me out, because i'm working towards his/her as well as my own goal."
hm, this might have gotten way more complicated than i intended it to be, still, yes, you can change, heck, it's tiring but i dunno, some things are kinda worth it