Do I need to strip current hair color?

If you apply the new color to your hair, you will have band of noticeable color where the old one grew out. If I were you, I would grow out your hair (just a few haircuts) then use the new color. Because your hair is chemically lighter than your natural color, you cannot strip out the color. When you are lightening your hair, it is impossible to strip out old color. It would be a completely different story if your hair was colored darker than your natural color. Then a color remover would come into play