Brunette and going lighter...

Hi all, I really appreciate any help I can get with this....

My natural hair color is dark sandy blonde/light brown even.  About a year and a half ago I dyed it dark brown with a semi-permanent color.  It faded but not entirely and when I wanted to go back to my natural color I had it done at a salon, where I got all over blonde highlights, which I've been getting about every 3 months for the past year or so.
About a month and a half ago I dyed my hair again, the same dark brunette color with the same semi-permanent dye I had used before. 
Now I want to go lighter, more to my natural color and with highlights, but I don't have the money to get it done at a salon so I was wondering how difficult it would be to do it myself.  My hair now, since the color has faded a bit, is about a medium-light brown (looks a lot lighter in the light, you can see my highlights coming through as well).  My mom has used at-home highlighting kits for years and I've used them as well so I'm comfortable doing that myself, and I've dyed my hair darker myself too obviously, but I've never gone lighter with dark hair so I don't know how that works.  I'm afraid of something horrible happening and ending up with orange hair...
I would figure I'd need to dye all over with a dark blonde or light brown and then do the highlights, but I really don't know so that's why I'm here.  Any suggestions on how to go about this?   Thanks so much.

Tracy