To delete an entry from the history, e.g. because it contains a username or password, show all history entries by typing
in the command line and then delete the entry with the -d parameter by specifying the history number, for example
history -d 498
to delete line 498. Then save the change with
If you do not save the change, the command would still be visible if you run the history command in a new shell. In newer versions of the Bash shell you can just put a space in front of the command and the command will not be stored in the history.