The very first version of dbui used the following cask:

brew tap kenanbek/dbui https://github.com/KenanBek/dbui

Now it is changed to https://github.com/kenanbek/dbui (KenanBek -> kenanbek).

But it turns out that the cask's URL is case-sensitive, hence

https://github.com/KenanBek/dbui != https://github.com/kenanbek/dbui

And this prevents upgrade to the new versions.

To fix this, you will need to first uninstall dbui:

brew uninstall dbui

And then, untap kenanbek/dbui:

brew untap kenanbek/dbui

After this is done, try to tap and install with the most recent version:

brew tap kenanbek/dbui https://github.com/kenanbek/dbui
brew install dbui

Once this is done, all future version might be install (upgraded) with brew upgrade dbui.