Htc 626s need help

THIS IS MY GETVAR DETAILS
(bootloader) version:0.5
(bootloader) ramdump-mode:false
(bootloader) variant:MTP eMMC
(bootloader) secure:yes
(bootloader) version-baseband:
(bootloader) version-bootloader:
(bootloader) max-download-size: 0x10000000
(bootloader) partition-type:cache:ext4
(bootloader) partition-size:cache: 0x10000000
(bootloader) partition-type:userdata:ext4
(bootloader) partition-size:userdata: 0xf0000000
(bootloader) partition-type:system:ext4
(bootloader) partition-size:system: 0xa0000000
(bootloader) serialno:HT61SB003484
all:
finished. total time: 0.149s
I NEED TO DOWNGRADE TO 5.1.1 TO BE ABLE TO UNLOCK BUT I DONT KNOW HOW TO PUSH MIST.IMG SO IT KEEPS GIVING ME ERROR WEN UPDATING. PLS I NEED GUIDE AND HELP. THANKS