There are two ways to change the A records in the WHM interface:
1)To edit the DNS zone manually and change the A records for the domain, use WHM's Edit DNS Zone interface (Home >> DNS Functions >> Edit DNS Zone) to edit the desired zone.
2) To cause your server to use A records that point to another server whenever you create DNS zones, use WHM's Edit Zone Templates interface (Home >> DNS Functions >> Edit Zone Template) to modify the DNS zone template.