I found a lot of examples on how to change the username for specific revisions and so on.
But what I need is this: I did a checkout with the authentication credentia
Go to Tortoise SVN --> Settings --> Saved Data.
There is an option to clear Authentication Data, click on the clear button, and it will allow you to select which connection you wanted to clear userid/pwd for.
After you do this, any checkout or update activity, it will reprompt for the userid and password.