If you know your current password, but would just like to change it you can do so from the Account Settings page.
How to reset your forgotten password
If you've forgotten you password you can reset it as described in this guide
You can reset your password from the login page.
VegPlotter will then ask you to enter your email address or username.
Once provided an email will be sent to you with a link. This link will open a page where you can enter a new password.