Most likely the trading bot uses the api key and secret to do automated trading.
You need to look at the documentation of the specific exchange on how api key are created and deleted.
Then just delete the current api key and secret.
Regarding changing the password - it is of no use.
Most exchanges use 2 levels authentication, with the 2nd level being sms or google authenticator. A bot does not have access to the 2nd level and can not log in into an account.
