Although it isn't possible to uninstall a preloaded app from your device, you can disable it to prevent it from loading on your device.
- First, go to your Android Settings.
- Under Security, tap Device administrators and uncheck the box next to Lookout.
- Then, in the main Android Settings find Apps.
- Tap Lookout and choose "Force Stop"
- Tap Storage then "Clear Data"
- Lastly, click the back button and tap "Disable"
Some more background:
For some users Lookout is preloaded on their device and it is therefore considered a system app, the same as Facebook, Flickr, Google Maps, and many others. System apps cannot be uninstalled from a non-rooted device. You can validate this by going into the "Manage Applications" setting and choosing "Lookout" or "Google Maps." You will see that neither provides an uninstall option (other than uninstall updates).
If you have gone to the Google Play Store and updated Lookout from there you can remove those updates from your phone, but not the base app itself. Again, this works the same way for all system apps.