If you want to flash a custom ROM on your Android smartphone or tablet you need a custom recovery. Many people appreciate Android as a platform because it offers the ability to modify the system without needing much skill. Android Wear is a new platform that Google built for wearable devices and it essentially functions the same way. Developers have already started creating custom ROMs and now custom recoveries for Android Wear smartwatches have cropped up in due time.
TWRP or Team Win Recovery Project and CWM or ClockworkMod Recovery are two of the most widely used custom recoveries on Android smartphones and watches. Both of them are now available for the LG G Watch as well as the Samsung Gear Live.
The procedure is quite similar to how you would flash a custom recovery on an Android device. The boot loader needs to be unlocked first before the recovery can be installed. Once the recovery has been installed you can flash custom firmware, wipe the device and access several advanced system functions.
Do keep in mind though that there are risks involved if you tinker with the OS at this level. So make sure to read up before you try anything you have never done before.