For upgrade go to terminal in android studio and type 'flutter upgrade' it will automatically pick latest version with stable channel
If you have updated flutter, after upgrade run flutter doctor. and in flutter doctor if you see error like 'license status unknown' then run 'flutter doctor --android-licenses'.
Go to sdk manager from upper right corner, then go to android sdk and then uncheck 'hide obsolete package' then check 'android sdk command line tool latest' then apply and then OK. it will download latest version.
Now run flutter doctor again your error will be removed