You will need a COMPUTER WITH WINDOWS SYSTEM, A MALE TO MALE USB CABLE,  A NEEDLE to press the reset button.  

1- Install USB driver (to make sure this step, can un-install the USB driver fast, and then install). 

2-Ran "RKBatchTool.exe"-Choose the language

3-load FW

4-Load box

Use a needle to press the reset button and do NOT release, connect your box (usb host) and computer with usb cable, press power on, than the RKBatchTool.exe will detect your box and turn green, then release "reset", press upgrade. 

5-Then the box is updating until it shows below, the whole process is finished.

The newest version for KT-611 is Android 5.1, below you can find everything you need for the FW updates of KT-611

FW for Android5.1

http://www.mediafire.com/file/2zm2yyucr9ma6tj/KT-611.zip

FW for android6.0

https://drive.google.com/open?id=0B8EphDfonBmGSFRDQnR4ZHdVUE0

Batch tool and USB driver

https://www.mediafire.com/?zi7f2qwgvc7msc0  

Below is the demo video for your reference, 

https://youtu.be/FIhOLILglQ0

FW for KT-608, 609, please download from below link, 

http://www.mediafire.com/file/6a04sh35tdxobg4/update_F5_kt6xx_20150915.zip