Use apksigner from the Android SDK build-tools to sign and zipalign the file.
Download the main "UCCW - Ultimate custom widget" app from the Google Play Store. Download uccw495 sign apk
Open the UCCW app, go to Settings > Backup/Restore, and select the downloaded skin file to import it. Use apksigner from the Android SDK build-tools to
Use a tool like apk-signer from the Google Play Store. go to Settings > Backup/Restore
If the skin comes as an APK file (or you are customizing an APK), you may need to sign it to install it on your device.
Download the specific skin file (often a .uzip file) you wish to use.