The OBDPEAK K2 has had minor hardware iterations over its manufacturing lifecycle. Using firmware meant for a different version or a different brand (like Jansite or Imagebon) can permanently brick your device. Always verify your specific hardware version with the seller.
Since the K2 doesn't usually support Over-The-Air (OTA) updates via Wi-Fi, you have to do it via a microSD card:
Extract the downloaded firmware ZIP folder onto your local hard drive.