Once you have logged in to the site, enter the page Account settings, click the button 'Freeze my account', and choose the reoson.
After freezing the account, no one can see you any more on the website nor your previous activity.
To delete your account, press on the button 'Delete My Account' on the same page, enter your password and choose the reason. Notice that you can't reactivate your account after deletion.

Enter the page Forgot your password and enter the email you have registered with.
In the email that you received, click on the link, which will direct you to a page informing you about your new password.