Move client new WMS server

Hi

I'd like to be able to move our thin clients from old WMS 1.4 server to new WMS 3.2 server. I don't need to import/export the database as we have a simple thin client configuration.

On my test vLan DHCP scope I change Options 165 & 166 to point to the new server on 443 & 1883. I don't want to use DHCP option 161 (ftp/http/https server hosting ini file) at all, as we don't have a spare server to run IIS website on and we can do everything we need with WMS rather than using ini files hosted on a "file server". 

When I unregister and restart the thin client it just ends up back on the old WMS server. I've tried a factory restore too.

What do I need to do to register the thin client on the new WMS server?

Thanks.