In watchOS 6, you can finally delete some of the stock apps from your watch. If you don’t need them, and don’t want them cluttering up your watch, you can remove some apps. This is the same process you can use to delete third-party apps that you’ve added to your Apple Watch, though you can do the latter in the Watch app on your iPhone; you cannot delete stock apps in the Watch app, for some reason.
To do this, press the digital crown to display your apps.
If your apps display in list view, press and hold the list until you see this:
Tap Grid View; you’ll see your apps in a grid:
Lightly tap and hold on any app until the icons wiggle, as they do on iOS:
Tap the small x icon to delete an app.
As you can see here, you cannot delete all the stock Apple apps. For example, you cannot delete Mail, Phone, Calendar, News, etc. You cannot even delete the Stocks app. You can delete apps such as Noise, Period Tracker, Timer, Alarm, and Stopwatch, but not World Clock, Calculator, or Reminders. So you may be able to lighten up your app list a bit, but not by a lot.