Google recently released the Lollipop update (5.0.1) for Android Wear devices and it is now rolling on the Sony SmartWatch 3. One of the big new improvements in this update is the ability to load new watch faces. The Android Wear app for phones was also updated recently to make switching watch faces more easily. Click here for a selection of free and premium watch faces curated by Google.
The Lollipop SW3 update can be downloaded by anyone running a phone with Android 4.3 and above. The update is being pushed by Google so you will have to wait for it to hit over-the-air (OTA). Alternatively you can try to load the software manually via the OTA zip file, click the source link for the download info.