Welcome to the forum!
Before flashing your device, please make sure that you can live with the issues that you see here. They are being fixed by the developer working on the Nexus 4, but you should be aware of them before flashing.
You will need to reflash your phone in order to update to our builds. Please ensure that you back up your data before continuing. There are instructions for backing up and restoring your data on this wiki page. After you've finished that, follow the instructions on the device page to flash Ubuntu Touch.