I have medium brown hair. I'd like to color it an ash blond. Will I have to use bleach?

probably not

I have medium brown hair. I'd like to color it an ash blond. Will I have to use bleach?

Does anyone even use bleach any more? More than likely if you used bleach you would get some funky orangish color instead of blonde. Try asking your stylist for advice if you don't want them to color it. Usually if your hair isn't super dark you don't have to strip it before dying it ash blonde.