How do I delete an app from my watch to provide enough space for an update

In addition to what the others have said, to Free-Up Storage

For songs, see the "Remove music from Apple Watch" section in:

Add music to Apple Watch - Apple Support

and for pictures, see the "Limit photo storage on Apple Watch section in:

Choose a photo album and manage storage on Apple Watch - Apple Support

Also, try unpairing and pairing your watch again and restoring from the backup just created in the unpairing process. This deletes all temp and corrupted files and re-indexes the file system. In some cases, this can free a lot of storage.

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

Also see:

If you don’t have enough space to update your Apple Watch - Apple Support

Remove an app from Apple Watch

• Grid view: On the Home Screen, touch and hold the app icon until you see an X on the icon, then tap the X to remove the app from your Apple Watch. It remains on your paired iPhone, unless you delete it there, too.
• List view: Swipe the app left, then tap  to remove it from your Apple Watch. It remains on your paired iPhone, unless you delete it there, too.

Note: Not all builtin apps can be deleted.

Go into the Watch app on your iPhone, scroll down to the “Installed on Apple Watch” section, click into the apps that you want to remove (you have to do this one by one), then turn off the “Show App on Apple Watch” button, this uninstalls the app.