Your Lightstream Account can be accessed by signing into your Twitch Account from studio.golightstream.com, which will automatically added as a destination. In addition, you can now sign in using your email address that is related to your account as a different option if you prefer.
Please note that if you sign up with your Twitch account and you need to sign back into your Lightstream account, then you would need to select the Twitch option again and sign in with your Twitch credentials. If you try signing in using the email option (even if that email is the same as the one used on your Twitch account) this would lead to a second account being created since your each option on the login screen is treated as a different login method.
If you happen to accidently create a second account with us my accident, you can delete that account by clicking on the Lightstream logo at the top-left of the screen and click on the "Account Settings" option and you'll have an option there to delete the account if needed!