You can lighten your hair quite a bit if you spritz it with lemon juice and go out in the sunlight (this is an old trick my grandmother taught me, and works best in summer). If you want to darken it...
These products usually has its instruction on how to use effectively, your result would vary greatly on how you execute the process. there a lot of brands you can choose from like loreal, Wella hair...
There is no real way to dye your hair without some sort or hair dye. if you are uncomfortable using a permanent dye there are temporary ones that last about a week, but these are hard to come by and...