You are constrained by your ISP if you require a static IP address ~ most ISPs have to use dynamic IP and DNS server addressing for network operational efficiencies.
If this download program requires you to have a static IP address for your WAN gateway;
1) be cautious as to why it does
2) look for another ISP who will provide you with a static IP.
Re-validate why you need to change your internet access/service provider as well as your network setup, just to be able to use one download program.