Whenever you login with Google Authenticator enabled, you are prompted to use your authentication code to login.  Underneath the entry field for your code , there is a link entitled "If you lost your Google Authenticator device, click here to disable Google Authenticator authentication."  Clicking this link will send an e-mail to your LastPass account e-mail address (or security e-mail address if you have set one), that will contain a link that will temporarily disable your Google Authenticator.   If you are unable to access your e-mail for some reason, and have lost your Authenticator device, please contact LastPass support.