Minecraft wiki entry for Updating_old_terrain, associated text: 1 Non-breaking update
1.1 Using MCA Selector (any Java)
1.2 Using MCEdit (1.7.2-1.12.2)
1.3 Using the tools
1.3.1 Preparation
1.3.2 Protecting regions of your world
1.3.2.1 Example
1.3.3 Running the selection
2 Breaking change
2.1 Splicing by Y
3 Gallery
4 References