If your hair hasn't been dyed before and the color you desire is less than three levels lighter than your current hair color, you can use a dye instead of bleach. For three levels of lightening or more, bleach is more reliable.
If you've dyed your hair previously, you will generally need to use bleach to lighten your hair regardless of what color you want, because dye can't remove dye.
Before You Bleach
You should have a goal in mind before bleaching your hair. By combining the concept of depth levels and the lifting potential of the different peroxide concentrations, you should arrive at an estimate of how much lift you can achieve when bleaching your hair, and this will help you avoid mistakes and not hold unrealistic expectations when you use the product.
If you are not sure you could safely bleach at home we recommend you let a professional hairdresser do the bleaching and then use ColoConditioner for colouring or toning at home.