In order to change you have to be able to adjust your thoughts and often your beliefs (not an easy thing to do). You have to modify your habits too. After all, a habit is a sequence of actions or thoughts that are just repeated over and over again. It's kind of like Pavlov's dogs where they respond with salivation to the ringing of the bell. I bet when you get up in the a.m. you have the exact same sequence of events - you get up, go to the bathroom, brush your teeth, wash your face, maybe take a shower, maybe put some clothes on etc. Each one of us has some variation on this theme that is repeated every day. Why do we do the same things over and over and over again? It's easy and keeps us in a comfort zone. If we had to think about doing things in a different order every day, that would require more thinking and energy and probably inject some additional stress into your life that you don't need.
Any kind of change requires a rewiring in your life - whether it's in your thoughts, feelings, actions or both. So if you feel you're resistant to change, try to go deep within yourself and see if you can figure out what it is in your life that would be altered. Once you identify those areas, it might be easier for you to accept the modification in your lifestyle. If you can look at the change in a stepwise manner, you might be able to approach it with less fear. I think that when we don't really know what differences in our lives a particular change is going to make, then the fear mounts and our resistance increases. But if you can break down the dynamics of the change and what it will entail for you, then you can meet it head on and the fear won't be as much of a factor.
Sometimes we're not ready to accept change because we think that to make the change will be the same as admitting we are wrong, not as smart as the person who proposed the change or in some other way inferior. It can be pretty scary to mix up our lives and force us out of our routine. After all, how many times have you heard (or said) "it's worked ok for all these years, why change now?". That's just a defense mechanism to keep us from having to put any effort into doing things a different way and also admit that we could have been doing something better or more efficiently. To many people, admitting that is equivalent to admitting that they've been wrong and stupid. It's not that at all. A fresh set of eyes always helps see how things can be done in a different way. It doesn't mean that any one is dumb or stupid. That's the first thing to remember when you're starting to feel defensive when you are approached with a change recommendation.
Bottom line, if you don't feel that you're ready for change, dig deep inside yourself to analyze why you are resisting. This is key to understanding what's going on in your head and in subsequently figuring out how to embrace it instead of pushing it away.