The homescreen of your Apple watch is too crowded? You can always free up some space by hiding apps you rarely or never use.
Tap on Digital Crown to view your installed apps. Press and hold on the apps icons until they start to jiggle, but don't press to hard or it might trigger the Force Touch gesture of the Apple Watch, which is unwanted in our situation.
Tap on the small x button appearing next to any app icon to hide the latter from your homescreen. It should be noted that stock apps (Siri, Music, Passbook...) can't be removed and thus don't have the x button displayed next to their respective icons. Repeat the operation to hide more apps if needed.
Removing an app from the homescreen of your Apple Watch doesn't necessarily means that it has been permanently deleted. The app is still available on the paired iPhone and you can restore it at any moment. On your iPhone, open the Apple Watch app and select the My Watch tab to get a list of all your installed apps. Select an app that you have previously removed from the homescreen of your Apple Watch and Toggle the Show App on Apple Watch switch On: