Hair dye help?

k i reciently(month ago) got my hair dyed its blonde with lots of dark brown and reddish streaks on top its pretty cool and i liked it but my hair grows pretty fast and my roots are starting to show i wan tto go back to being just blonde i dont want to go to the hair dresser i wanna do it at home what would happen if i just dyed it blonde like from the box? would it look dum because of the black or would it kinda just look the same only lighter?