Answer by mikyll98 for Flutter upgrade error: Unknown flutter tag

You need to call flutter upgrade from Flutter install directory.

To find its location, you can use which command on Linux systems:

mikyll@debian-EQPNRAP:~$ which flutter/home/mikyll/Programs/flutter/bin/flutter

And where on Windows (or which aswell if you have it installed):

C:\Users\mikyll\Desktop>where flutter C:\Program Files\flutter\bin\flutterC:\Program Files\flutter\bin\flutter.bat

Once you found it, you can change directory and finally call flutter upgrade:

$ cd /path/to/flutter/$ flutter upgrade