I am planning a name change for the same reasons - hate my birth name! I have one of those names that people almost always shorten without asking. I NEVER use the shortened form but people use it all the time. It's what family always called me, mother still does. I'm at the point where hearing it nearly makes me feel physically ill. Of course, I can't say anything to her because she is perfect and Never did Anything - I'm just a liar. Please don't ask me why she is still in my life.
I've asked my closest friends to use my chosen name now and that helps. Names are so powerful and if the one you have has horrible associations then I support you changing it!