Look at the status squares at the bottom of the tool. If your device is connected correctly, (in Batch Tool) or indicate "Found One LOADER Device" (in AndroidTool).
For a major version upgrade like jumping from Android 4.4 to 5.1, always click instead of "Upgrade." The Restore option formats the NAND flash, erasing old system remnants to prevent boot loops. rk3188 android 5.1 firmware
Install Drivers: Run the Driver Assistant and click "Install Driver" to prepare your PC. Look at the status squares at the bottom of the tool
Quad-core ARM Cortex-A9, typically clocked at 1.6GHz (up to 1.8GHz). rk3188 android 5.1 firmware
Browse and select your downloaded .img Android 5.1 firmware file.