The way I do it [from the terminal]:
List possible timezones
timedatectl list-timezones
Pick a timezone from the list
timedatectl set-timezone "[timezone]"
[replace timezone with the timezone you picked]
And finally, set the time
timedatectl set-time "yyyy-MM-dd hh:mm:ss"
y is each digit of the year
M is month
d is day
h is hours
m is minutes
s is seconds
Hope this helps 