Highlights / Notes
Faster map-data format, animated textures, refactored map-updates and world/dimension-handling,
new map-storage implementation AND BlueMap-native addons! =)

Upgrading from 5.0 or 5.1
You were already using the latest 5.x snapshot/rc?
Then don't have to do anything! Just replace the .jar-file

Upgrading from any other version (3.x or 4.x)
A clean re-installation is highly recommended! You WILL need to re-render all your maps.

• Shut down your server
• Make a backup
• Delete your current BlueMap-??-??.jar
• Delete the BlueMap config directory (./plugins/BlueMap or ./config/bluemap, depending on your platform)
• Delete the BlueMap data directory (the ./bluemap folder in your server root)
• Delete any existing BlueMap-databases (All tables on your db starting with bluemap_, only if you were using an sql-storage)
• Follow the usual installation steps

If you are using an external webserver or any other custom setup:
Revisit the wiki-pages and update your configuration accordingly!
Relevant changes:

• The .json.gz files are now .prbm.gz files
• The textures.json is now also compressed (textures.json.gz)
• The sql-tables have changed and the sql.php got updated accordingly

Changelog since 5.1

• Updated sponge to SpongeAPI 11
• Fixed CLI still generating the old resourcepacks folder

Changelog since 3.21 (condensed)

• Switched hires-model format from json to a custom binary format: prbm (slightly modified version of prwm)
  • Massive performance improvement when loading map-tiles in the browser
  • Slightly smaller on the storage
  • Slightly faster to render
• Added animated textures
• Refactored Chunk-Loading and World management
  • Added dimension config to the map configs
  • Removed world-sky-light config from the map configs
• Full rewrite of the map-updating system
  • Chunk change detection is now fully based on chunk-timestamps instead a mix with region-timestamps
  • BlueMap will now delete already rendered parts of the map if the world got trimmed or chunks got otherwise removed from the world
  • Changing the map-edges is now possible without purging the map
  • Added command to force-update only map-tiles on map-edges
  • Added debug command for checking map-tile states
• Correctly separated ResourcePacks and DataPacks
  • Biomes are now fully DataPack based (internally)
  • Renamed resourcepacks folder to packs (still accepting both, resource- and data-packs)
  • Removed support for bluemaps biomes.json file in resource/data-packs (use the datapack format to configure custom biomes)
• Full map-storage implementation rewrite
• Add first implementation of a native-addon loader
  • Addon devs now have the ability to make their addon loadable by bluemap directly instead of depending on a mod/plugin loader
  • A limited version of the API is now also available on the CLI implementation, which can be used with native addons
  • Addons can also make use of BlueMapCore and BlueMapCommon for extended functionality
  • Native addons are EXPERIMENTAL right now
• Downloading vanilla-resources now considers all available minecraft versions
• Added support for nested resourcepacks (introduced in 1.20.2)
• Added resources for signs, hanging-signs, banners, shulker-chests, bell, mob/player-heads, (decorated-)pots and cake
  (thanks to @TyBraniff, #536)
• Allow texture-variables with missing # in certain situations to align with vanilla behaviour
  (fixes loading of some resourcepacks/mods) (thanks to @glorantq, #525)
• Removed the pretty-printing from the settings.json to discourage editing it manually
• Added -m flag to the cli which allows to specify certain maps that should be rendered
• Added -e flag to the cli which works similar as -f but only forces updating map-tiles on map-edges
• Add option to display chunk-borders on the map (thanks to @TechnicJelle, #542)
• Map-settings now load in parallel to speed up initial page-loading with many maps (thanks to @Salzian, #538)
• Added/Updated serbian, ukraine, russian, finnish, turkish, french and zh_CN translations
• Fixed render-issues with custom world-heights
• Fixed empty block-states having the wrong block-properties
• Fixed lowres-heightmaps not working below y0
• Fixed an error with self-healing when a textures file is corrupted
• Fixed unlisted markers being counted in the marker-set gui
• Fixed sql.php port config not being used
• Fixed grass-sides sometimes not being colored correctly (#492)
• Fixed popup-marker sometimes hiding behind other markers
• Fixed flickering with some animated textures introduced in 4.1
• Fixed webapp menu-title of player-markers not translatable

Full Changelog
https://github.com/BlueMap-Minecraft/BlueMap/releases/tag/v5.2