If the blonde hair colour you bought states that it lightens by up to 3 shades, that means natural hair, not dyed hair. Definitely do a strand test. If the strand test is a fail, you’ll have to strip the ash brown dye with a colour stripper. I’ve used Scott Cornwall Decolour Stripper from Priceline & I’ve recommended it to heaps of people on the forum & a family member. The Decolour Stripper removes hair dye & your natural pigment, or there’s the Decolour Remover, which only removes dye. Only downside is the price, $25ish.
The pics are from the Priceline website. Old packaging on the left, new on the right. Top shows the Stripper, below is the Remover.