@willian Upgrade will rewrite the DHCP config of your FOG server. So make a backup copy if you have modified it.
I could even clone the server for testing but later I will see how I do.
As well make sure you read und understand this before you upgrade: https://forums.fogproject.org/topic/13488/fog-1-5-7-officially-released
Is there any important information in this topic about this issue? I read everything but I saw nothing related.