You won't see any difference if you just slap new dye on top of the old one, unless it's a radically different shade and darker/same color depth level. You'll need to remove dye from your hair if you want to make it lighter (there are special procedures for that).
Another thing is, you won't get the exact shade that is on the cover. Dyes react with each other and your hair's own pigment. If that sakura shade has too much red pigment you may get the unpleasant result of it mixing with your current shade.
Also... I'd advise against using non-professional dyes. Especially if you do it often. You'll end up with your hair packed with pigment that might become impossible to remove later, if you decide to go light blonde for instance.
Now me, I'm a hairstylist myself and have a very short hair cut so I can dye it anything I want and whenever I feel like. I go from red to blonde and back on a whim. But I use professional dyes of course and I know how to care for my hair properly so I don't kill it dead.