help needed!

Is the dark brown hair colour dyed? If so then you should use a colour remover up to three times to get the dye out, which will give you a good base for dark red. (Colour removers are not damaging so your hair's condition will not be compromised.

If your hair is natural under the black cherry then I would suggest using colour removers and fading treatments such as anti dandruff shampoo and washing up liquid then doing a mild bleach bath at least a week later to get your hair to a gingery lighter brown colour which will be light enough to achieve a dark red over with a semi permanent dye.

Dark brown was a dyed colour, but from now what should I do? I got suggested to go over with the same box dye? Would this help at all? My roots are a nice red colour but it kind of blends to black ish purple, how can i come from this to a deep red? Thankyou for the advice above

Nope, use a colour remover like colour b4 up to 3 times which will give you a lighter base to work with. Going over with the same box dye won't work. You need a lighter base.

Then use a semi permanent dark red dye which will give you a much better result than a box dye.

Agree with everything Marthakins says.