Here (or skip if you've already activated it in the past). Same for doughnuts / Peeping Tom in the appropriate place on the Options screen. Like WT, skip if you've already done it before.
Notice: All official guides are included in the repack but if you want to get just them you can get them all in below link.
Official Guides (Chapter 2, v0.02) =
Mainly 3 reasons:
1. You need to move over to a new version, because of poor programming and you need a fresh start.
2. Image/video assets become too large and the game begins requiring about 5-6 GBs of space.
3. You plan on releasing episodic versions to steam.