First off, it's called Blockland Launcher r1690, not V21.
Secondly, you don't have to re-download, you just have to open Blockland and update it.
Also:
If you were experiencing the bug where Blockland just crashes when you open it, it should be fixed now.
BUG: The update caused people to crash when the game was in full screen. Badspot fixed the problem three hours ago.