they cannot be deleted unless they are abusive, in which case they would need to be flagged by users and a review moderator will need to decide on whether it breaks the review guidelines or not.
If they aren't abusive, your best bet is simply to bury them under helpful new reviews.
You could try PMing an administrator if you gave out your personal information or identifying characteristics with non-savory remarks in each review that you think might be detrimental in a job interview or something, but they might not do it if you don't have a good reason. Since the minimum age for an account is 13, there are a lot of us with embarrassing reviews or forum posts we wish we could delete but can't.
