百度出來的命令是這樣的：brew cask upgrade
然后得出的反饋是這樣的：Error: Unknown command: upgrade

解決：
brew cask --help
得到：

Commands:

    --version              displays the Homebrew-Cask version
    audit                  verifies installability of Casks
    cat                    dump raw source of the given Cask to the standard output
    cleanup                cleans up cached downloads and tracker symlinks
    create                 creates the given Cask and opens it in an editor
    doctor                 checks for configuration issues
    edit                   edits the given Cask
    fetch                  downloads remote application files to local cache
    home                   opens the homepage of the given Cask
    info                   displays information about the given Cask
    install                installs the given Cask
    list                   with no args, lists installed Casks; given installed Casks, lists staged files
    outdated               list the outdated installed Casks
    reinstall              reinstalls the given Cask
    search                 searches all known Casks
    style                  checks Cask style using RuboCop
    uninstall              uninstalls the given Cask
    zap                    zaps all files associated with the given Cask

耐心看下去會發(fā)現(xiàn)一個這樣的命令：reinstall

嘗試：brew cask reinstall qq
成功。

學(xué)到的是：正確的途徑學(xué)習(xí)獲取知識。