How can I change my hair colour the safest way?

I've died my hair about 15 times, with semi permanents and permanent dies. About 3 months ago I tried going back to my natural colour, a medium to light ash blonde. BUt, the hairdresser died it dark red/brown. It has faded to a medium ash blonde, but still kind of reddish, almost brown looking. My roots look lighter and more blonde. I'd like the rest of my hair to appear more golden or neutral blonde. Any suggestions on how to do this without destroying my hair, which is a little bit on the thin side, but still pretty healthy? I really don't want to put my head into the hands of another hairdresser, that I don't know, without some basic knowledge myself.
How can I change my hair colour the safest way?
Just do it yourself at home, buy a box from the store of the color of your choice and do it yourself. My mom does it all the time and it works great for her, and on the other hand my grandmother gets it done by a hairdressser and it works great for her too but she knows both of the haiirdressers very well(she has 2 hairdressers) and theyre great friends, so i still suggest you do it at home. I'ts cheaper and may be more trustworthy and realiable,if you don't like it just buy another color and do it over the wrong color to ease it down a bit to a better color. :) hope i helped