I need hair colour advice from someone in the know

[DextersMistress]

Natural colour is dark brown. I've spent years throwing box colours on, mostly reds. A few weeks ago after deciding I wanted to go light brown I went to my local college for a colour correction. They did:

2xbleach washes on length of hair but not the roots (first stopped working so was washed off and another applied)

Dyed it brown (roots were done in a slightly different shade, I think 6 and 6N were used)
I was left with quite a nice colour, although the red was still there. Roots were brown.

Now, I want it doing again and a friend of a friend is dyeing it for me but I need to get the colours myself from a professional wholesale place and I've no idea what to get/what will work.
Will it need bleaching again before a light brown will take? What about the roots? I'm clueless, please help.