Toners can only neutralize unwanted shades from your hair, but they alone do NOT lighten your hair, (except for a very minimal amount).
If you have dark blonde hair, for example, and you would like to go platinum blonde , you have to pre-lighten (bleach) your hair to a level 10 first. The bleaching will uncover the underlying pigment of your hair, which is pale yellow in this case. The final step is to use a violet based toner, for example Wella Color Charm T18 Lightest Ash Blonde , to cancel out the unwanted yellow tones.
If your hair a dark blonde/light brown level 6-7 and you would like a to get an ashy light blonde (level 8), you also need to pre-lighten your hair first. Aim to bleach to a level 8. The exposed underlying pigment will be yellow-orange. To neutralize the brassy shade, you can use Wella Color Charm 8A/740.5 Light Ash Blonde , for example. It is blue-based and removes the orange from your hair, with the result of a gorgeous ash blonde.
In conclusion, the key is to lighten your hair to the required level first, and then use a toner to neutralize the unwanted shades and get the beautiful shade that you were looking for.