Hi, Tara-J!
Have you tried deleting apps from your Apple Watch as well?
If this still doesn't allow you to update your Apple Watch, you may need to unpair it from your iPhone. This will wipe all data off your watch, but before unpairing, iPhone will create a backup of your watch for you. You can restore the data after you've updated your watch.
To unpair your Apple Watch, follow these steps:
1. Keep your Apple Watch and iPhone close together as you unpair them.
2. Open the Watch app on your iPhone.
3. Go to the My Watch tab and tap All Watches at the top of the screen.
4. Tap the info button next to the watch that you want to unpair.
5. Tap Unpair Apple Watch.
6. For GPS + Cellular models, choose to keep your cellular plan.
7. Tap again to confirm.
(If your Apple Watch storage is full - Apple Support)
After this is complete, you should set up your watch as a new one and then update after it's all done setting up.
To restore from the backup you created before unpairing, unpair your Apple Watch once more. However, instead of setting it up as a new watch, restore from the backup you created.
Have a great day!