Put DOWN the 40vol - that stuff will be more likely to burn your scalp right off your skull. Reddish brown will lift just fine with 20vol, it just takes a couple of sessions to strip the red tones out.
My advice is to do it over the space of a few weeks - use semi-permanent colours in between to 'match' to the current shade, itms. Do a bleach with 20vol and powder (mixed 50/50), then a conditioning treatment, tone if necessary, and when you can see what colour it comes out, get a semi in a shade or two darker and put that on, and leave it for a few days. Then repeat that process until you achieve your desired result.
Pro-tip: avoid Schwarzkopf dyes like the plague. I've tried different brands from Schwarzkopf and had nothing but trouble - two incorrect colours (wrongly labelled, I'm guessing, one was a pharmacy issue as that batch number had been recalled as the batch was faulty, and then last night I used a platinum beige blonde and ended up brown, wth! Heads-up, it was labelled Napro, I didn't realise it was a Schwarzkopf), and another that I used a few times but it just fried my hair even when washing it out long before the recommended developing time. Ugh!

I was blonde until last night, it's taken a few months (but I was stripping out black, which is crazy hard unless you know what you're doing) and then intense red, which is also tricky. Once I got to a nice blonde with bleach, I'd cover it with a box of blonde dye in the shade I wanted so it didn't come out all bogan-brassy Good luck!