- The release notes
Links for downloading Krita 5.1.0 are available in the above link and from the official download page.
A 5 minute video with some of the new features: Everything new in Krita 5.1.0
And one, much improved tool, worth mentioning: The Levels filter can now work, individually, on R, G, B, RGBA, Alpha and Lightness channels.
Official Websites