Check the docs for a list of steps:
Also change location / to location ~^/
Our instance got upgraded (for reasons) from a 1.13 release to 1.14.0-7.
Would there be any danger in going back down to the last stable release in 1.13? I guess I'm concerned about any potential DB "schema" changes that might have occurred when we upgraded to 1.14.
[edited to fix version numbers...Fridays, eh?]
The only schema change in 1.14.0 is https://github.com/NodeBB/NodeBB/blob/master/src/upgrades/1.14.0/fix_category_image_field.js, at worst you would have broken category background images.