If your RK3188 device is currently sluggish on Android 4.2 or 4.4, moving to a refined 5.1 firmware is the single best way to maintain its utility as a media center or light emulation station. By stripping away factory limitations, these "better" builds unlock the true potential of the quad-core silicon.
Updating an RK3188 device requires specific tools, usually the or Android Tool . rk3188+android+51+firmware+better
To help you find the file for your hardware, could you tell me: If your RK3188 device is currently sluggish on Android 4