There are two ways to update the server address in the enabler. The first would be to push out a network profile and select the Manage WLAN IP Settings. In the WLAN IP Settings tab there is a Server Address setting. This is the address the devices will attempt to connect to. The network profile has the highest priority as far as in the enabler so if you have a current network profile with the server address this will be the only way you can change the ip on the device.
The second method to change the enablers server address, if you do not have a network profile, is to use an enabler config package. This is a software package where you can configure the settings of the enabler from the server. The latest enabler config packages are available on the download site from the following link : http://www.wavelink.com/Download-Avalanche-Enablers-Software
You also have the option of creating a Scan to Configure Document from a Network Profile that includes the Avalanche server address so that you can migrate the devices one by one if you want that level of control. This gives you the control of knowing that you are not interrupting a user working by forcing the update over the air as you will be manually scanning a set of barcodes on each device.
Another alternate approach depending on if you have a new enough existing implementation of Avalanche is using a Mobile Device Profile to selectively push the server address to devices based on any selection criteria.
Glad I could be of help!