Deleting your account is a permanent task and so when done, your collection will not be recoverable. For this reason, you need to be certain that you want to delete your account. This is different that deleting your Collection.
To delete your account on the web app, simply click on your profile picture in the top left corner (it may be a blank grey circle if you have not yet uploaded an image). Once there, on the bottom left, you will see a button that says, “Delete Account”. Since this is a non-reversible function, you will be prompted to confirm your selection.