Remove all chunks except spawn and change world type (from default to amplified)

Solution 1:

I decided to just have a go after piecing together a basic understanding from googling, and see what would happen. Here's how I did it. (I'm not sure if each step is necesary or correct but it seems to have worked)

• Load the world. Visit each thing I want to keep and place or remove a block (to force a save of that region)
• Close and save.
• Make a backup of the save folder (just in case)
• Delete ALL of the 'MCA' files in the 'regions' folder that don't have today's date on them (or all the ones that have a date older than the recent visit to the world)
• Using 'NBTexplorer' go into the level.dat->data folder and change 'generatorName' to 'amplified' then save.

See from the picture below that it worked.