Today, Apple seeded iOS 8.1 and is now available for download. There are two ways you can download the software update: via over-the-air (OTA) update or via iTunes. To download over-the-air, just go to Settings > General > Software Update. You will be required to free up some space [at least 1.6GB for iPhone 5C] of your compatible iOS device's storage while if you update via iTunes, you will only be required 86.6 MB [the actual size of the software] to update.
Here are the screenshots of the changelog of the update: