need help with php errror

[[DEV]AlphaOMEGA]

Warning: strftime() [function.strftime]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for '-4.0/DST' instead in C:\xampp\htdocs\register.php on line 39

umm how do i change the php time zone so this error doesnt happen

[pieter]