I haven't found a guide yet that's written specifically for FO4 but the same basic steps apply as for previous Beth games. You can either make a Steam Backup which will only backup core game files from original installation, delete your entire game folder, and restore from the backup. Also be sure to backup and remove your save games and .ini files in My Documents/My Games/Fallout4. For a more 'manual' method: In Fallout4/Data/ folder (where all mods except loaders/injectors, script extenders are stored), delete all folders and files except the base game files - keep the Video folder, and any .ba2 files, and files beginning with "Fallout4 -" i.e. "Fallout4 - Meshes.ba2". In the base game folder make sure you delete any ENB or other custom loaders, injectors, etc. Here's a tool posted by a member of the Nexus that will clean your data folder of anything but vanilla files: Fallout 4 Data Folder Scrubber by ShadowReign Productions http://www.nexusmods.com/fallout4/mods/153/? Good luck, my recommendation is to always keep backups :o)