How can I safely change hair color back to blonde from brunette at home?

I was a level 10 blonde before dyeing my hair a level 4 dark brown (permanent) at home in March this year. I am naturally a dark ash blonde. I decided in May that I wanted to return to blonde and went to the salon. They would only give me partial highlights, so I ended up with highlights of light blonde, caramel and copper on top, with the dark brown underneath.



Yesterday I decided to try lightening overall on my own at home. I had about 6-7 weeks of grow out of my natural dark ash blonde color. I used a level 10 feria in light cool blonde in this attempt. Unfortunately, it barely lightened the already colored hair, however it did lighten my 6 weeks of grown out roots! Since I used a cool blonde, I didn't end up with orange roots, but my hair definitely has a golden blonde tone, especially on the roots and the top half of my head that has the highlights.



So after all of that background info, here is my question...hopefully to a hair colorist or expert home hair colorist out there: What should I do from here to get to blonde again? Should I try using an actual bleach blonding kit? Do some heavy duty conditioning treatments beforehand?
How can I safely change hair color back to blonde from brunette at home?
wash it,put in the color.it.s in a bottle