Basically I dyed my hair a dark brown and it looks horrible on me, I have tried washing it out but its not working. Do you think I would be able to bleach it and then dye it a light brown?

This is possible if you use a toner with a neutral tint. Anything else will result in the wrong color. You don't need to prebleach. There is no need to do this. If you dye light brown you may end up with a reddish tinge unless you use toner with a neutral tint.