can anyone tell me how to delete changeset comments in a way that historical comments are not show anymore?
I don’t know any, and with this post you also asked anybody to find out where your garden is 
too true
You can contact https://wiki.openstreetmap.org/wiki/Data_working_group to request deletion of personal data in OSM’s database.
+1
Data Working Group people can “hide” various bits of information, including notes and changeset discussion comments (which I presume is what is being requested here). We can also redact data from the OSM database, but not the comment added when a changeset was saved - but if that is needed we can have a chat with the site admins about it.
- Andy (from the DWG)