You should login or register.
You can do this by sending an email to firstname.lastname@example.org, but the easiest way is to visit the Lyft Support Page. Once you’re on the page, you should see the following form prompting you to create a new support request. You’ll need to enter the email address and phone number associated with your Lyft account, as well as a subject for your request (something simple such as “Deleting my account” will be fine). You’ll then need to choose to delete your account under “What can we help you with?” To do this, click on the arrow to the right of the box and then click on “Profile and account setting. Then, click on “Delete my account or unsubscribe.”