change "VPN device IP address"

Hi,

A while ago i configured a Virtual Network, with a VPN gateway to connect to our vm's in Azure. Everything went well and worked as expected. Now we are moving to a different ISP for our Internet line, so our public IP address changes. 

Were can I change the IP address of the "VPN device IP address". The IP address you enter when you create the Virtual Network...

Thanks,

Sven.