You must have PRAW and Python installed. A device with good bandwidth is recommended.
Clone this repo, cd in to it and run python main.py.
This script will first take your Reddit Username, Password, Client ID and Client Secret. Click here to find out how to get/make your ID and Secret.
You then need to input what you want to delete (c for comments, p for posts) then the score thershold for those submissions. For example, entering 100 will remove all comments/posts with 100 or less points.
Obviously this only works on your own account. There is a maximum limit of 1000 submissions per run.