let’s have an experiment. starting with this:
[admin@MikroTik] > sys resource pr
uptime: 3m32s
version: 6.30rc20
build-time: Jun/12/2015 14:48:23
free-memory: 231.6MiB
total-memory: 249.7MiB
cpu: Intel(R)
cpu-count: 2
cpu-frequency: 2933MHz
cpu-load: 0%
free-hdd-space: 73.4MiB
total-hdd-space: 99.1MiB
write-sect-since-reboot: 514
write-sect-total: 514
architecture-name: x86
board-name: x86
platform: MikroTik
upgrade it to v6.31:
[admin@MikroTik] > sys resource print
uptime: 55s
version: 6.31
build-time: Aug/14/2015 15:42:51
free-memory: 233.8MiB
total-memory: 250.0MiB
cpu: Intel(R)
cpu-count: 1
cpu-frequency: 2933MHz
cpu-load: 0%
free-hdd-space: 65.6MiB
total-hdd-space: 99.1MiB
write-sect-since-reboot: 614
write-sect-total: 614
architecture-name: x86
board-name: x86
platform: MikroTik
(look at ‘cpu-count: 1’ - probably, that’s the reason why download links for that version don’t work)
go to System → Resource → Hardware - check ‘Allow x86-64’ (in WinBox. can’t find it in CLI). reboot
and voila!.. oops, ‘architecture-name: x86’ 
no worry, just upgrade to the latest version:
[admin@MikroTik] > /sys resource print
uptime: 1m24s
version: 6.38.3 (stable)
build-time: Feb/07/2017 09:52:42
free-memory: 200.2MiB
total-memory: 221.8MiB
cpu: Intel(R)
cpu-count: 2
cpu-frequency: 2933MHz
cpu-load: 0%
free-hdd-space: 66.5MiB
total-hdd-space: 99.2MiB
write-sect-since-reboot: 708
write-sect-total: 708
architecture-name: x86_64
board-name: x86
platform: MikroTik