A VIVO instance can be configured to use Internal or External Authentication. If it is configured to use Internal Authentication, once when you are logged in, you can edit your user account.
Moreover, the VIVO instance can be configured to allow users to initialize resetting its own password. In that case, login dialog includes 'I forgot my password' as it is shown below.
By clicking at the link I forgot my password the following form is open.
After filling this form, an email will be sent to user account with the instructions how to reset the password.