So, deleting from ripper store? Or deleting from VRC?
I can help if you're deleting from VRC, their website lets you delete it, or otherwise I believe you can delete from the VRC SDK menu in Unity, but I'd recommend using the site. Open the site, login, on the left (if using a computer) find 'Avatars', select the name of the avatar you want gone, then click delete avatar! Easy.
If you're deleting from ripper store, I have no information for you, hopefully someone else can help.