Amlogic Mbox question topic

I love this little TV box but, I have two issues... This box of marketed as being able to handle 4k content but when I played a mkv file that was 30 gb in size the video was very choppy... any one else noticed during with very large video files?

Second issue is that I would like to change WiFi dns of the device but can't see option to do this as per normal android options

Appreciate any help thanks

Ps: dear moderator please move this post of there is a better sub section thanks