Hello Maylin125,
I understand the update on your Apple Watch is taking longer than expected to complete. I'm happy to help you out with this.
It's not abnormal for an update to take some time to complete. The amount of time it takes can be affected by various different factors including but not limited to your Wi-Fi connection speed and how busy the Apple servers. My recommendation is to continue to wait and allow the update to complete on its own. Although you may see it display many hours or days until the update is expected to complete, you may also see this go do drastically without any action taken on your part.
If the update still hasn’t completed since you submitted your post in Apple Support Communities yesterday, try disabling Bluetooth on the iPhone your watch is connected to. Make sure you do this in Settings > Bluetooth, and not in Control Center. This could help speed things up by allowing your iPhone to focus solely on the Wi-Fi connection and not Bluetooth. Also, make sure your iPhone is up to date too: Update your iPhone, iPad, or iPod touch. Additional, you can try connecting limiting the amount of devices connected to your Wi-Fi router while the Apple Watch update completes. Even though you may have a fast internet connection, multiple devices connected to the same Wi-Fi router at the same time can slow things down.
Thanks for using Apple Support Communities.
Take care.